It is not "GAY" to give your a hand job or to even go down on him. If you and your friend are enjoying this activity with one another who's to say it's GAY?
Now if you put your heart into it, let's say you confuse the sexual act with Love then you might want to question it yourself. Sexual activity between consenting adults is the norm.
But again, if you find yourself falling for him you may want to take 3 steps back and regroup.
I have had sexual relations with the same sex and not get involved. It's just sex. It's just having fun!
Listen, buddy, I'm not saying you, with your "100%" str8 are gay (although I'd question that in anyone), but that is a gay act. Particularly the going down part. Just sayin.