Heh. There are -millions- of opinions about it, if you go looking for it.
As for helping you with a rebuttal, read on:
http://www.11points.com/Books/11_Things_The_Bible_Bans,_But_You_Do_Anyway
EDIT: Homosexuality isn't wrong. It is both normal and natural, and anyone who says otherwise cannot...
Telling him you're not interested in him is perfectly legitimate, and not a lie. You don't have to explain yourself at all.
You're doing him a big favor. Trust me.