ESH (except for the BF).

I assume it was all about the money and that was all it was for you but I feel that by hiding this from your boyfriend, knowing this may hurt him, you have damaged his trust in your relationship. He maybe thinking what else you have kept from him because of this. It's going to be hard to rebuild this relationship, especially as he has to still see his "friends" at school, who I believe don't seem to care about him.

As the friend put up the painting knowing your bf would likely see it, I feel like these friends have played a prank on your boyfriend and you fell for it. They may say it was non sexual in front of you but when you are not there they are probably giving him a lot of abuse about seeing you naked. Sadly there are people in this world that don't have much empathy and I think your bf needs new friends.

Even if I am mistaken, you and his friends should have known how he would feel about this. I think you and his friends knew this would hurt him but both wanted this to happen and didn't want your bf knowing so he couldn't have to chance to object to this.