You should never be in a bed with a child who is not blood-related with you. Doing so leaves you open to all sorts of accusations. Ask your SO how he'd feel if bm had his daughter in bed with her and her bf.

He also needs to understand that you are his gf, his daughter already has a mother.  Besides that, when she's on his visitation time, it's to spend time with HIM. You are not a substitute parent for her.

Understand that you can support him in his role as a father. Why do you feel he should be supporting you?  Is he heaping responsibility for his daughter on you? Not your job.

Your bigger problem is your SO being dismissive of your concerns. It shouldn't matter what you are concerned about in the relationship, he shouldn't dismiss it. It sounds like he wants you to be a "replacement" Mom when his daughter is there, and that is not working for you as his daughter already has a Mom. You need to figure out what you are comfortable with and then let him know. If he isn't ok with your boundries, you need to rethink the relationship.

Your SO has his daughter 85% of the time and wants her in bed with you, wants you to say I love you, and doesn't understand why you have reservations. Does he let you make decisions as much as he and BM do? Do you have equal say as to when she comes over on BM's time? Can you make decisions about discipline?

This guy is delusional. He wants you to "be mommy" when it comes to you doing certain things, but not others. That's not how it works. You won't develop parental feelings without the entire experience of being a parent. From my experience, adoptive parents develop those feelings but most stepparents don't. That's because they are not allowed the full parent experience. They are expected to do certain things but prevented from doing others. Told "don't overstep, you aren't the parent." That's when resentment develops. 

 he can be dismissive when I bring up any topic that relates to the dynamic or how things are between the 3 of us in the house....I can't bring things up without being made out to be over dramatic or him being dismissive and defensive. 

Huge red flag if you cannot discuss these things with him. It's important for the relationship to have this discussion.

I've also noticed that generally, when it's us 2 we're absolutely grand and get along fine. When it becomes a 3, it's total. Disney Dad and I'm ousted and just to go along with whatever

Another red flag. He shouldn't treat you differently or oust you when his daughter is around. 

It sounds like he needs to remain single for awhile and just focus on raising his daughter (nothing wrong with that). Any woman that he is with, is going to get the short end of the stick. Don't let that woman be you.

I remember my DH telling me that if he had gotten full or majority custody of his daughter (she was barely 5 when he and BM split) that he would not have gotten into a relationship with me. I thought it was a weird thing to say but after reading a lot of stories on this site, I get it. He knew that she would need a lot of his attention and it wouldn't have been fair to me.

If your BF can't balance parenthood and a relationship, he should at least be honest about it.

I'm going to be the odd one out here. I broke up with a guy who was awesome. But didn't have dad vibe. He was great for me, but not for my reality.. me and kids. My (now) DH of 20+ years had kids. We parented the same. Our kids jumped in bed with us, For nightmares, or for good morning snuggles. I signed up to be Mom2. He was Dad2. 
if you're not on the same page, willing to be Mom, ask yourself..,is this the relationship for you? Some folks do well with disengaging. That was never an option for us. We both committed to each other and our kids. It sounds like your SO wants you to be Mom, heart and soul. My DH and I had the same expectations. Your not wrong if you don't want to. But he isn't either. 
Figure out each others expectations and boundaries, then put emotions aside and make decisions based on reality.

if you don't want to Mom kids, maybe this is not your relationship.

RUN

Oh, never, ever sleep in bed with another man OR womans child.

Establish, publish, and enforce standards of behavior and standards of performance for any spawn in your home. Regardless of kid biology.

If you do not, it will only degrade from where things currently are.

You do not have to have papers with daddy to do this. It is your life, your home (you live there), and your standards.  Daddy can either enforce them or GTF out of your way while you do it. Do not give him/them any other choice.

Do not sacrifice yourself on the altar of Sparental martyrdom to a failed family which includes a prior breeder mate and their baggage.

This will never change. Your SO is looking for that "Happy Family". What he created in his mind. What has nothing to do with real life.  He's never going to find it and it's all your fault that life doesn't go his way.  He actually disrecepting you. He telling you he the boss in the relationship. If you don't comply he will pick up his kid shd leave.  
Having a kid 85% of the time where he shouting you out.  Questions why are you staying for.?  To be beat up 85% of the time. 
'You just can't live this way. It's inky going to get worst. When SD realize the power she controls.  Time to make a exit plan. Its time for DH to have another failed relationship and marrage.  Do you see a pattern here.

This isn't really a "step" problem - this is a problem with your partner.  He's dismissing your concerns,  "punishing" you, ignoring your boundaries and not treating you like the priority you should be.  Sure, the issues come up the most regarding his daughter, but they'd be there anyway.  

When I first met my husband, SDs were 1 and 4 and they slept with him every night he had them.  I told him I was not sleeping with unrelated children and if he wanted me to ever stay over his kids had to be in their own beds. Guess what? He had those kids sleeping in their own beds in less than a week.  He didn't dismiss my concerns, he addressed them.  Same with excessive BM contact; boundary was put in place and respected.  This is not to say that my DH is without fault or that steplife is great - not at all - but the relationship was worth pursuing because he was willing to deal with issues, take my concerns seriously and prioritize me and our relationship.  It doesn't sound like that's the case with your boyfriend.  I'm guessing it's not steplife, it's HIM. I'd give some thought to throwing this one back. 

There bed room ..is there bedroom,, This is there  private space in the home. SK are not allowed in the master bed room,  SK are not allowing to go through the draws ;. Closets.l touch the makeup. .Some SM will put a lock on door..

When a person goes into a second marrage. It's going to be different then when two people have bio kids. Your DH must understand that his concept of the big happy family is gone,,it was lost in the divorce 

A Step"parent" is allowed to do, and help, and love, and PAY as long as you do not also try to have any kind of authority.

I suggest you read around on here.