I'm an adopter not an adoptee but I have a difficult relationship with my father who walked out when I was an adult and disappeared dropping our previously close relationship like the proverbial hot brick (presumably in favour of his new woman).
When he finally resurfaced (after about 2 years) he completely ignored me, his behaviour was truly awful - not calling or finding out how I was when I was in hospital having a biopsy done for cancer, ignoring my letter to say I was adopting DS.
This went on for ten years.
I have relatively recently reconnected with him and am taking things very cautiously but he seems to be fine with DS and has stuck to our agreed meetings about quarterly.
I was very angry with him and very conflicted about how I felt and seeing him again and had some counselling. The counselor (not unreasonably) asked me ideally what I would like from our relationship now.
It took me a while to think it through but eventually what I said to her was "What I want is the father I deserve not the one I've got"
She found this a tad unhelpful! 
But bizarrely it really helped something click in my own head. That I did deserve better and the fact that I wasn't going to get it wasn't my fault - it was just the way he is. I have emotionally disengaged from him, I now see him, have a pleasant enough relationship with him but it really isn't a parental one (to me). I can't fix him, I can't make him behave in the way that I think he should, I do deserve better but I have made peace with that fact and it doesn't rock my emotional stability anymore.
Mind you it's taken over 12 years to reach this point of calm acceptance with a functioning though somewhat emotionally unsatisfying relationship so don;t be tough on yourself about how conflicted you feel or how up and down you feel or in fact anything you feel. There really isn't a blueprint for how to deal with this kind of situation.
Hope you don;t mind me sticking my oar in.