your boyfriend has naked pictures of his sister... on xbox?

i’ve been dating my best friends little brother for 6 years. my boyfriend recently started using nude pics for the background on his xbox. the pics he stole off his sister's phone are of her. i know she would be pissed if she knew that he had her naked on display for everyone that comes over to see. should i tell her what he's done or try to talk to him about it? they are full brother and sister so the whole thing is really rather gross. i know people have fantasies but i think this is going a little too far. also he is an angry asshole and doesn't like to be questioned which is why i haven't said anything about it yet.

let’s start with what i think is the most concerning part of your question and work from there:  your boyfriend is an ‘angry asshole’ who doesn’t like to be questioned.  i’m very worried that this is a relationship that you’re not in voluntarily.  there is not one positive word about this boyfriend in your entire question the negative words that show up are very strong ones. 

you need to get out of this relationship.  if what you’ve said is true, that he’s an angry asshole who is incapable of communicating, then this is a terrible situation for you to be in.  if you said what you said out of anger, then he clearly knows how to push your buttons in a way that’s just as unhealthy.  and if you feel like you can’t get out of this relationship, then you need to reach out to your family and friends for help, because it will get worse.  he will escalate the situation as time goes on. 

and you need to tell your best friend that this is going on.  immediately.  uncomfortable taboo aside, this is a huge and unforgivable violation of your best friend’s privacy.  and the longer this photo is up, the less likely it will be that you will ever be able to get it off of the internet.  someone might take a picture of it while he’s out of the room.  they might share it.  her name, and possibly the circumstances of it, might become attached to it and it could follow her around forever.  please, for the sake of your friend, tell her about this right now.  

and tell her you’re dumping her brother.  if he is the sort of unreasonable rage-filled person that you’ve described, having his family on your side will be very helpful, particularly if he takes it upon himself to harass you after you’ve broken up.  plus, provided there is any part of you left that still cares about this boy, they may be able to help him get the help that he so clearly and desperately needs.