l'd like to return him the favor but...

So here's a short story... this dude I've been dating for about 4 months, we have awesome sex, he's cute, he makes me cum a lot, and he also cums about 3 times the days we see each other, I'd like to make him happy because he makes me happy. But he has also said he likes to get cut in his back and that that makes him excited while having sex. Aaand here's where it gets a bit creepy for me. He has his back all scratched and with scars from previous cuts and wounds. He has once said that it would be hot if I cut him with a razorblade or knife or so. Would you? I feel a bit bad not for myself, I'm not afraid of blood or anything but it stills a wound... I wouldn't like to hurt him... What would you do?