The 'in your face' feeling of '3rd wheel' takes a long time to diminish. I don't think it will ever disappear but it can be something that is livable and will not take front seat in your psyche. The more fun and positive memories you share as a trio will help create your own unique family bond. The 'external' to bio feeling you have will never go away but it can be something you can accept.
Here are some things that will help diminish the 3rd wheel feeling over time (years):Be Invited:
Ask your partner to include you in things like doing at home activities. For example if they are doing a puzzle and he notices you are not doing it with them he should say "want to join us"? Being invited by my partner was important when I felt like the 3rd wheel at times. Also it is important to give the girl her daddy time. Ask you man to 'over-communicate' in including you when appropriate. I felt as though I needed to be 'invited' for randomly banal things for quite some time.Get Respect:
It is concerning that she treats you with disrespect. I hope that the dad holds his daughter accountable to be respectful to you (he should require she responds to a 'hi' or 'goodbye'). If he doesn't you need to discuss this with him so he holds his daughter accountable. If he doesn't support or enforce simple respect your issue is more with him than with her. You also need to set boundaries for yourself requiring respect. This doesn't mean you need to be mean when you communicate - just be gentle but firm. For example, "I'm sorry but I can't get you x or do x when you speak to me that way. Can you try again?" If she says 'no' or throws a fit then just say "I'm sorry I can't help out right now." If Daddy is present he should support your request for respect and not just do his girl's bidding if she turns to him. You need his backing of respect for things to work. She will try these boundaries and you two need to be united.Show Love & Interest
: What is key? Cultivating and working at a relationship with this girl. Yes it hurts when she doesn't say 'hi', sit in your lap, give you running hugs, etc. However, that is why you are the adult and you need to build the bridge to her. You chose to be in her life. She didn't choose you. You just appeared one day and you take up Dad's time! (This, however does not justify rude behavior.) Make it safe and loving for her to bond with you in her own way. Go out of your way to show love to and include her. Hug her. Let her know she’s special – tell her you love her (if you do). Offer to read stories or color with her. Example: I say "I love you" to my stepson every night he's with us and I hear it back from him about 1 or maybe 2x per year (we have 50/50 custody so I see him a lot). He is 10. I've known him since 5 yrs old. He isn't an expressive kid - but I hear him say it to his dad lots more (obviously). However, when he does say it - I glow inside. Give love when you don't get it back. Keep giving. Turn to your partner for support. Will this be hard at times? Tiring? Yes. However, you are investing in your family and in your future.
One thing you can't do is just dig your feet in and say 'I'm not going anywhere' and 'put up with it' if you want things to change for the better. The girl will pick up on the negative or passive energy which won't endear her to you. I’m confident this approach will eventually strain your relationship with your fiancé. This method is also emotionally tiring (i.e. bathroom breakdowns) and isn't realistically sustainable for the long haul if you want to be happy in your marriage. You aren't just marrying your man. You are marrying your man and
his daughter - both require love and commitment for a blended family to work.