D.B.
ETA: I just read your "So What Happened" and I am really alarmed by what you are saying. Your boyfriend is extremely controlling - you aren't "Allowed" to take vacation, you aren't "allowed" to talk to the child's mother (which by itself isn't a huge problem, but it is along with everything else), you are required to take the daughter shopping and do her hair. He skips ahead with his daughter and your little boy can't keep up - yet instead of making your own way, you feel heartbroken. You've lost your way, my dear. You have no rights, and you are desperate to have any sign of affection from this man for you and your son, no matter what happens to his daughter. And although he only has his daughter 4 days a month and insists on you taking her out of there for part of it, he wants custody? He's using you to be the "perfect mommy" as if he thinks that will help his case. It won't. You're being used. And you already say counseling won't work. Get out. Now. Get counseling for yourself to learn to make better choices. I don't know if you'll go back over older responses so I hope new responders will tell you to do so and tell you this sounds like very controlling behavior.
Original: You feel out of place…because you are out of place. Your boyfriend doesn’t know how to parent, and if he sees his daughter so infrequently, it’s almost impossible to learn.
If she’s with him so rarely, I am baffled about why he spends that time with you at your house. This child needs her father. She’s already transitioning from Mom’s house to Dad’s, but no, you add in your house, you and your son too. No wonder she’s confused.
Should she be kicking you? No, of course not. But why is she with her father so rarely, and when she is, he’s snuggling on the couch with you? And why are you feeling insecure and resentful? She’s 10. She’s struggling. If he can’t talk to her aunt without her having a hissy fit, he needs to deal with that. You cannot bridge that gap and “make her feel included.” She’s either included by him, or she’s not. If she’s not, he’s screwing up and you cannot fix it.
I think you (and your boyfriend) might want to consider updating your attitude about what girls need. You seem to think there are “girl activities” like shopping and hair brushing. That’s pretty antiquated – at least until you know this girl a whole lot more than you do. Just because you like braiding or shopping doesn’t mean she does. And if she’s shopping with you, she’s not with her father – which defeats the purpose of visitation.
I’d say to back off. Be 200% more patient than you are now. Let them have dad/daughter time at his place, not yours. Learn to be without him 2 weekends a month. Stop with holidays and vacations. You’re forcing this girl into relationships she’s not ready to have. Wait 2 months – then consider a children’s museum or a picnic or a hike together, without hand-holding or kissing. Just be an adult in her life, and not a needy girlfriend (which is how she will see you).
Your boyfriend needs a parenting class. And you could benefit from one as well, so you learn more about the developmental stages of a 10 year old. If you don’t do this now, she’ll be in puberty in a year or so, and it will be so much worse. You two are jumping the gun, and you are more concerned with her adapting to your relationship that you are with you adapting to her reality. I’m a stepmom, and I can tell you this situation is doomed if you don’t back off.
You don’t have to dote on her and be her maid. But you cannot be her competition either. And you should not be with her when he’s not there – that will solve the problem of kicking and denying. I have no idea why he is abdicating his responsibility and making you handle her, but I can see why she’d resent it.