As a girlfriend from a long-distance boyfriend that has called celebrities/fictional characters hot around him (but he doesn't mind), this is absolutely terrible.

You have to know the difference with finding actual close people you know IRL hot around your partner, and calling celebrities/fictional characters that too. There is no problem when it comes to celebrities or fictional characters, but if you actually know that person and talk to them, it's time to split ways.

If he's still open even if it's a closed relationship, is friends with plenty of his exes, tries to follow most of your female friends and no male friends, just because they have revealing profile pictures, EVEN send screenshots of sweet messages they sent him, I'm sorry, but I think the best thing you have to do is break up. If your feelings are being ruined by him (as you mentioned you are extremely insecure), you have to let him stop beating the dead horse and show him what you've got. Plan some revenge, or snap the shit out of him! That'll get him to cry during the break up. Best of luck!