but he's my friend

does sex with a long time friend drastically change the friendship? if so how?

Yes, it can. Sex and Love BEFORE the commitment generally don't mix. Some people say that when they ALREADY love someone, having sex with that other person just INTENSIFIES their love for that other person. But then you have alot of friendships that are never the same once sex has become the basis for the "thing" that's going on between you & that other person. The reason SEX can ruin a long friendship is because in general, most "friends" don't have sex just once or twice; they normally start slowly having sex more & more often to the point that it becomes almost expected. But don't get me wrong, if the connection & chemistry is there & both people have talked about it BEFORE the moment (sex) actually happens, there is more than likely a better chance that things will turn out just fine. But always know, friends don't have sex with eachother & when they do, most of the time atleast ONE of the 2 people in the friendship changes, even if it's just a little bit. It would be one thing to have sex with someone one time because "things just happened" BUT don't fool yourself. You have to question yourself as to WHY the thought of 2 people that have been good friends for so long (without the sex) are suddenly having these feelings? And of course you have to rule out all the possible changes that can and WILL occur once it's too late (once you've already had sex with them)...Not all cases end in the friendship strictly being about sex or being ruined completely. There's always those people in the world who have proved reality wrong. But REALITY says in order to keep it a friendship, maintain the friendship in a "friendship manner"

thanks for the advice.

but what about the saying friends before lovers?

It works best for aqua. I just wouldnt recommend the friends with benefits route. Someone always gets hurt.