TELL YOUR DAUGHTERS. NOW. 

Normal 13-year-old boys don't grope sleeping girls. He's not sorry he did it, he's sorry and ashamed he got caught. Please, please, please tell your daughters. Women deal with enough sexual harassment in life, they don't need it in their own home from trusted family members. 

ETA: your husband needs to do some serious damage control. Normal curiosity is watching porn. It's not normal curiosity to grope your stepsister. I would consider what kind of man I'm married to if he was okay, or worse, downplaying this. He should have taught his son right in the first place! 

Increases geometrically when their is an unrelated male (either stepfather, or stepbrother would be considered unrelated for this purpose.  Do your DDs have their own rooms?  Share?  

I think BF is in denial.  13 is way too old to be curious.   This was way more than curiosity. 

I don't know if I would tell them specifically that he did this to someone, but I would have a conversation with them in general terms about not allowing any male to do that to them, PERIOD. That you want to know if this happens to them and they should feel free to punch the offender in the nose.

DH needs to take it seriously and have a discussion with his son about it.

I can't believe anyone is suggesting it's wrong to say what happened at BM's house. This isn't a matter of intruding on BM's home/privacy. It's a matter of protecting your children from sexual assault. You all know predators escalate, right? First it's a grope... then what? What's next now that he's gotten away with a grope on a sleeping girl? Holy shit. Tell your kids, fuck BM's privacy. 

I think that you should have a conversation about making sure that they are locking the door when they shower or change clothes. Rules need to be set and NOT EVER broken about bedroom spaces. Boys don't go into girls rooms. You need to have a talk with him and honestly let him know that you will forever have your eye on him and if he ever touches one of your daughters we won't be having a discussion- police will be called and he will find out what happens to little boys in prision for sexual assault. Touching is assault. 

A self defense class for the 3 of you wouldn't hurt. Your daughters are at/approaching dating ages and should be able to defend themselves- period. This doesn't have to be about SS but it isn't not about SS either. 

Make sure they have locks on their bedroom doors and tell them to use them. I realize this might make things a bit tense around the house, but their safety is what matters.

What is your boyfriend going to do about what happened? What is he going to do to make sure it doesn't happen again? A 13 year old boy who is curious about girls does not grope a sleeping girl. What he did is criminal and he could have been criminally charged.

I think you need to make sure your boyfriend is going to take this seriously and if he is not - you might need to reconsider having your girls live with his boy.

Absolutely tell your daughters that there is a potential sexual predator in their lives. And good for them if they tell him off about it. Someone has to teach him. If he’s not in counseling he should be ASAP. Sexual touching at 13 is not curiosity. He sexually assaulted a family member. He’s dangerous. 

You are definitely in the right. I hope the talk goes well, maybe you can post an update. 

did your SS stepdad ban him from the house?

I don't understand why there is a discussion about what to say to your daughters. What you should say is "pack up ladies, we're getting a condo!" This sexual predator with no impulse control is living with your daughters. There is no reason to warn them, to get them classss to defend against him, to make them lock their own door in their own home. He needs to be gone or you do.

I’m glad you are telling your girls.  

This 13 year old pervert committed sexual assault and until he has counseling and real consequences, he would not be allowed in my home period, especially if I had daughters.

I would be pressing assault charges if I was the mom of the stepdaughter too.  

He knowingly took advantage of another defenseless person for his own pleasure.  How is your husband ok with trying to hide it?  He needs to get the kid help.  Right now he is just coddling the pervert by giving him ‘talks’.  

We all know how effective those are.

If you insist on allowing him into your home, locks on every door, and as others have said, cameras in common areas and  let him know you and your daughters will take care of his issues with a smack down if he so much as bumps them, then you’ll call the police personally for good measure and will press charges. I’d say it in front of dear old dad too.

You and your daughters’ mental and physical safety must take priority over a clear, proven sexual predator.  I’d never trust this kid again.

the men in his life allowed him to with no repercussions.

Hugs for assaulting a sleeping girl? 

Good god woman.  This kid is doomed. Take your girls and get them out of this situation before he does something to them.

I'm sorry you're going through this. I can't imagine how difficult it is knowing you love your husband but his kid is a threat to yours. It's gotta be hard, but do what's best for your kids. If your husband doesn't appropriately resolve this, you need to leave. 

Your boyfriend's son didn't "invade his step-sister's privacy" - he sexually assaulted her. And your boyfriend's response was to tell him he screwed up and he should put it in his past. And the father of the victim talked to him and he him he loved him. So this young man has two grown men basically telling him what he did was not that big a deal and he should just move on.

I'm going to revise my advice. Take your girls and move out. Keep seeing your boyfriend if you want to, but don't make your girls live with a boy who has committed at least one sexual assault with no consequences.

It is beyond my understanding how the father of the victim has chosen not to defend and protect his daughter.

This is rape culture. Putting the onus on the girls to stay safe instead of making sure the boy doesn’t reoffend. How would that feel in your own home? To be charged with always locking your door? Taking self defense courses? Telling them not to let it happen? 

This is a teachable moment for everyone concerned. 

Put him in counsiling. NOT HUG HIM. Take away his privileges. Talk to law enforcement. Get a police officer to scare the hell out of him. Show him Juvie centres. Talk about consequences. 

I'm not an expert. They should talk to a person who specializes in rehabilitating teenaged sexual offenders. My cousin is one, and I could ask her what would work, if that would help. 

Will do

Definately tell your daughters.  Forewarned is forearmed. 

This kind of thing needs to be addressed extremely agressively so that it does not become a long term issue.

IMHO of course.

No personal experience with any of them - looked for non-profits and government programs

http://www.nyap.org/sex-offender-treatment-service/4576110432

https://www.crimesolutions.gov/PracticeDetails.aspx?ID=36

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2922753/

https://www.aamft.org/Consumer_Updates/Families_of_Juvenile_Sex_Offender...

PROTECT YOUR DAUGHTERS FIRST BEFORE ANY MAN, SKID OR ANYONE. I CANT STAND MY SD16 BUT I ALWAYS MADE SURE SHE DIDNT HAVE TO STAY WITH HER 14 YEAR OLD STEP BROTHER IN A 2 BDRM APARTMENT. IT'S INVASIBE FOR HER TO HAVE TO SLEEP ON THE COUCH OR SHARE A ROOM OR WHATEVER THEY DID WITH THEIR COMBINED 6 KIDS.

The fact that he did this while the girl was sleeping implies he knew it was wrong and thought the girl wouldn't know - very disturbing. He feels bad and ashamed 'that he got caught' - most likely not that he did it. I'd be very very careful about EVER leaving them alone together.

Children living without either parent (foster children) are 10 times more likely to be sexually abused than children who live with both biological parents. Children who live with a single parent that has a live-in partner are at the highest risk: they are 20 times more likely to be victims of sexual abuse than children living with both biological parents (Sedlack et al, 2010).                                                                                                                                                                                                                                                                Sedlak, A.J., Mettenburg, J., Basena, M., Petta, I., McPherson, K., Greene, A., and Li, S. (2010). Fourth National Incidence Study of Child Abuse and Neglect (NIS–4): Report to Congress, Executive Summary. Washington, DC: U.S. Department of Health and Human Services, Administration for Children and Families

SGS-now-12 showed concerning behavior @ 6 years old.  His bio-parents excused it, forgave it, laughed about it, minimized it & ignored it.  SGS's victims include neighborhood children and his cousins. The cousins were placed into foster care because their parents failed to protect them. 

You are at risk for losing your children. You are on notice.  You must protect them.  How? Well, that's up to you. 

From my experience, I would suggest that you seperate households and allow DH to focus upon helping his BS --- counseling & education for both of them.  My SO took a special class through CPS/court to teach him how to help SGS & keep other people safe, when they are at a public place.  Specialty help is available even in small towns & poor states.

You do not have to spend one second being concerned about how SS feels.  Your duty is to protect your daughters.

As Rags said forewarned is forearmed.  Your daughters MUST be told that SS has made inappropriate sexual advances toward another person.  You do not have to name who it is if you think you need to protect the victim's privacy.  But SS does not deserve any "protection" at all.  Let him rot.

 Your DH is worried that your daughters will not like SS because of this - well eff that.  SS deserves to be despised.

Tell your daughters, and not allow SS in your home untill he does some treatments, and he OK by a perfessional to be in your home.   That a start for now 

I suspect that you are also (maybe not consciously so) worried that, by telling your daughters you might get the kind of feedback that you are afraid to hear, i.e. that they have perhaps been assaulted to and haven't dared tell you ... Or  if not, that at least they can now express that they have felt uncomfortable around him for a while. I sincetrely hope this is not but it would be better to know.

Have you told them?