I'm with Sunshine, do your adoptive parents know that you know?
If not, talk to them, tell them how you find out and that you want to know all about it.
It don't always have to be painful you know.
It was their choice to adopt you, so they must have wanted a child badly and that child is you. They probably couldn't have a child of their own, but they did choose you and they love you, don't they, so I don't see the problem.
It's confusing right now, I know, but if you look into your heart, what difference does it really make if you love them too. You're not of their 'blood' so to speak, but they will always be the ones that raised you, worried about you, loved you, keep that in mind.
So try to talk to them in a honest way, for that they do deserve.
A rose is a rose is a rose...I guess...
Feel free to use the pictures on my website. http://communities.msn.com/Titiasplace/