Advice and opinions on tough issues needed!

I am a birthmother of a 15 year old daughter, in need of some advice from other birthmothers, birthfathers, adoptive parents, and adoptees! As shameful as this situation is, I need to straighten it out somehow...... At 17, I put my daughter up for adoption. My boyfriend of 2 1/2 years at the time was with me, and we picked out a family, met with them several times, and agreed to an open adoption. However, there was a chance (disclosed at the time to everyone) that my boyfriend was not the father. It didn't seem to be much of an issue. I think three of four of us wanted to pretend like it didn't matter, and my birthdaughter was never told. Instead, she was told that my boyfriend was the father, which we think he is. However, the (possible)birthfather has as of late decided that it is a big issue. The adoptive parents and I have encouraged him to have a relationship with her, especially because she is going through a tough time right now trying to figure out who she is--she has a lot of explosive anger, she is in therapy, and they are doing an excellent job of dealing with it best they can. She is an awesome kid, and I believe will make it through. But, he agreed at the time (though we were 17) that he would keep in contact, regardless of this situation. It is a very open adoption, I see her often, and it is very comfortable. However, he hasn't seen her since she was 3, and I (and the adoptive parents) think she needs to see him, or at least get a letter from him. He and I have been in contact, and his argument is that he feels he would be deceiving her if he were to see her and pretend that he is definately her birthfather. He thinks that she should be told now of the possibility that it is someone else. They and I don't think it is good timing, for a few reasons--what will it do to her sexuality? How will it complicate her life? Her sense of right and wrong? of deception? And, since they can't do a paternity test (the lawyer strictly forbid it til she is 18), they think it would just add animosity to the household. Also, their view is that sperm donor doesn't make that much difference; he is the one holding her in the pictures, holding my hand, at the birth, their in the first year of life, the one that loved and supported me. He feels that paternity is probably what matters most in finding out who she is, and swears that he has her best interest at heart--I think of him as a pretty stand up guy, so I don't doubt that he at least believes that. I have put myself in the middle, because I see both sides and because, ultimately, it is my fault we are in this mess in the first place. All of us want to do what is right for her, we just all see it differently. He says that he will talk to his therapist about it, and the parents say they will probably bring it to my birthdaughter's therapist for advice (after some prodding). I don't have a therapist (though maybe it's time....), and I am trying to figure out what is best for her, and maybe come up with some case studies and such. Any help or advice anyone can offer to this sticky situation would be appreciated!