i believe that it's possible that another relative intervened here. here's what i'm thinking.
another relative (perhaps one who is protective to you) had a conversation with your bio-dad about him being involved in your life.
since your bio-dad didn't raise you or have anything to do with you up until now, the other (protective) relative probably told him that they didn't think it was a good idea for him to create a relationship with you at this time.
it may be for reasons you do not (or could not) understand, like this relative may know that you are at an impressionable age, and that your bio-dad does drugs or something that maybe you wouldn't know...
what i would do if i was you is consider myself blessed. know that your bio-dad probably did mean what he said to you, but also know that God is out there protecting you. if HE intended for you to be with your bio-dad, He would make that happen. if not, then you're blessed by His grace and you won't be messed with any more.
i feel for you...i lost my mom at an early age (sort of the opposite situation you are in) and i really appreciate the value of a good parent. sounds like you have that in your adoptive parents though...so all is good (if not a bit confusing).
best wishes to you.
jasmine