Kids process things by acting out, playing, drawing. I think it sounds normal for a 10 yr old to be obsessed with death and blood... joking about it might be his way of processing this new knowledge. For what it's worth, my 3 year old tells me he's going to kill me a lot, I'm not worried about him turning into a psychopath, it's his way of dealing with anger and aggression. I feel very sorry for the boy, his parents are getting divorced, which is a horrible horrible thing to go through, he's most likely very angry about it but perhaps feels unsafe being angry with his parents, so you are getting the brunt. It actually might be a good reflection of your relationship, that he feels able express his emotions with you. You just need to maintain boundaries in a firm but kind way, not easy. Good luck!