Things sound tough for you mate, you may get a fair bit of stick from the lads here so I'm gonna try and give you some honest advice...
*Be thankful for the things you do have, I don't want to make light of your situation but by the sound of things - it could be worse, you're not starving somewhere in a third world country, you have your mind and your body, and you can put almost any problem right by using these things.
*I really know nothing about your woman problems, so I'll keep the advice general, I personally have no time for cheaters, and if you're suspicions are confirmed, move on (as hard as it is) you just don't need the aggro mate, life is too short, however, you need to confront her about this, you might just be having an attack of paranoia, and though it may be difficult to approach the subject be strong, there may well be nothing to worry about and it will be worth it.
*I can't offer much about your birthparent dillema, this may be something that stays with you for the rest of your life, and you may just need to accept it, which is a very healthy way of killing off impossible problems. As long as the family you are with, blood related or not, love you, you really can't complain.
I hope this helps, I really do. Remember, you can overcome almost any obstacle in life if you really try, stay true to yourself, find something you love to do which is creative or productive, find good people to share your life with. Some things we just get dealt in life, and though we may really hate them, there's nowt me can do, so even though you should never stop caring, please try to stop worrying, and enjoy what you have.