You've been given a gift.  He's left and now his kids can go.  This was never going to work.  It's hard to face a breakup but read around on here, you've dodged a bullet.  Good luck.

Rather than beg and plead for him to come back, celebrate that this failed partner and his failed family baggage are out of your life.  Good riddance.

Count your blessings. They are gone which is a huge win for you and for  your own teen.  A lying POS who manipulates her daddy to abandon his mate is not anyone you need or want in your life or polluting the life of your own still at home teen. 

Get on with living your best life.  They should not be any part of that other than fading into the past.

Take care of you.

in your home and by the very people that are supposed to love you. By the man whom you should expect to slay dragons for you. You've opened your home, your sanctuary to kids that aren't yours, which you didn't have to do. At all. The least that these teenagers can offer you is a bit of basic respect by following your house rules. 

You say he lacks empathy/sympathy towards you? Why are you making space for him in your precious life? We all only have limited time on this earth.

Having offered a gift like that, you're allowed to get mad when these kids act up, when they mess up or roll their eyes at you in your own home. If your dude AKA drama llama  storms out after his daughter says you went into her room and told to tidy up (true or not true - doesn't matter), he certainly won't be slaying any dragons for you and will most likely do a runner in the face of any hardship- you becoming ill, having a major financial loss etc.

And by then he will have used you up and sapped you of all your resources. Don't be a wife appliance that can be replaced.

It seems living with them is not what you thought it was going to be. That is ok. If things were a lot smoother before they all moved in then you can go back to that and you and your 19 year old an live in your house. When his kids are living independently you two could reassess the possibility of living together again. 

Having anyone move into your home can make you feel put out. I had a friend move in with me and my husband and sd during covid for one of the lockdowns so she wouldn't be on her own during that time. I felt put out having someone outside the family in our home. I got irritated by everything she did, even when she was just trying to help. She wasn't a messy teen moving all my stuff but it still upset the balance of the home for me. Things felt much better after she moved out.

On top of all that if you have ocd I can see why having someone upset your home could be extra distressing. 

I don't think your bf quite grasps the situation. They moved into your home. In your home, your rules go. Even if you HAD told his daughter to tidy her room, he should have told her to just do it - not storm off. 

If he truly wants to move back but his kids don't, they can stay with their mother and he can take his visitation elsewhere. OR he can get himself a place to stay, see his kids there, and continue to date you. You don't need to live under the same roof. Not sure I'd want him back though, he seems to put his kids on a pedestal and you're just expected to make do with the scraps. How old are these kids exactly?

Could you persuade your fiancè to engage in some couple's counselling? It seems a shame not to get everything out on the table with someone who could help before walking away? 

I think in these situations, you have to dig deep and work out if this is something you can live with? Is this someone you want to fight for (knowing all the baggage that comes with him) 

There are no easy answers to this but you both have to be very open and honest about your limitations. It feels like a lot to have 2 teen skids suddenly move in, is there room for compromise on his part? 

A house big enough for everyone to have their own bedroom. Having a living room, family room, and a crafting room,  starting fresh. You can set up household plans on. Making a list. Cleaning. Cooking, maintaining the house .  If SO can't afford this, then he should keep his mouth closed 

SO can not come into your home with his kids and want you to change.  You live this way for many years. 

GOOD

He gave you the biggest gift.

He prolly hoped you would be begging him back because this would give him the upper hand. He's toxic and so are his spawn.

If they cannot respect you in the home that you opened up for them then they have zero respect.

Frankly by him leaving is the best gift. Saves you the effort of  you eventually having to kick him and his toxic crew out.

Blessings

OCD isn't easy. I feel for you. I have a friend with it and her husband used to mess with things to annoy her (move things, shift pictures so they were not level, move her placemats). I found it incredibly childish and mean spirited.

What you're dealing with is worse. Your future spouse should have respected you and known what your triggers are.

However, there is also the part where you're supposed to work on your OCD tendencies so that everyone isn't ruled by them. The whole world doesn't have to conform to walk on eggshells because of your disorder. I'm assuming, of course, that you have a formal diagnosis and this isn't just about liking to have things your way and organized. If you have the diagnosis, others should be considerate while you're working on doing better. If it's just a matter of liking things the way you like them, then I think you need to pick your battles.

You do have a right to have order in your household, but you should be reasonable and flexible.

If you said things you shouldn't have said, then you should apologize and make amends.

At the end of the day, it seems he should be a better parent and fiance. And I think some time apart would be good for all concerned. Begging him to come back isn't the right course of action, though. It puts him in the power position AND it also doesn't allow enough time for you to examine the situation to see where you can improve and where you need him and his kids to improve.

Please do not have another thought about this guy.  He is not worthy of you.  Go with that.  Do not speak to him, do not re-engage with him.

When people demonstrate who they are, believe them.  

Get on with living your best life.  With the added benefit of knowing that living well is the best revenge. 

Enjoy living your revenge.

Take care of you.

This premise is a foundation of an amazing life of adventure and a love for the ages that I have with my wife.  My XW was serially adulterous.  She ended up, at least for a while, with the geriatric fortune 500 executive sugar/baby daddy who she was pregnant by when she moved out of our then recently purchased home. Over the next several months we worked through our divorce. She would drop a barb over how she was so enjoying socializing with people who had worked and lived internationally.

I had was raised overseas.  Yet, she was all puffed up by grandpa sugar/baby daddy formerly leading an international division for a large tech company and being the kitten arm candy for him while he was partying with his peers and their spouses.

Meanwhile back at the ranch and nearly 34 years later, my incredible bride and I have been married nearly 30 years, have lived on 3 different continents, traveled all over the world, have a wonderful marriage and life together, and have a great kid that we raised to viable successful adulthood.

XW... is at last count on DH #3 and all three of her kids are either cheat spawn and/or born oowl.  Grandpa Sugar/Baby daddy did marry her after their second child was born.  He also kicked her ass out and divorced her after she got knocked up by a boyfriend.

Blessedly I escaped without sullying my gene pool with her.

Go live your life of adventure and find your love for the ages. This guy is not that person.