What do you do when your boyfriend starts acting strange?

honestly, this guy is totally on the untrustworthy list from what you just said. I would say. quit talking to him. let her cheat on her boyfriend with this guy, he will get tired of her, if she's a bitch, she's a bitch, they'll use her for sex and then leave her. as for u, if you move on, you can find a cooler guy you can trust, and let her take all the losers. better he does end up with her and then you get with him and he cheats on you. right? you'll regret that, and she will think its hillarious if she's an enemy. so yea, play it off like ur not into him. if a guy likes you, he acts like a friend to you, and friends don't like people that don't like their other friends, thus, he wouldn't be talkin to her, you see.

Well if he doesn't have the respect to make you comfortable by not making contact with your enemy, then he doesn't have the respect to be with you. Ask him questions, examine his body language, study his facial expressions and if he gets upset with you for the questions. That should give you the answer you are looking for.

I'm currently with a guy who loves flirting because that's just who he is. I'm secure enough to know that at the end of the day its me who he wants to hold. So if you're having doubts about you're guy than why are you with him? It seems like he wants drama. She's just doing this to get back at HER boyfriend for being a flirt.

I would personally not be in a relationship with a guy like that. I don't like drama personally so I would just end it. If you really like him talk to him about it and find out what his motives are for acting like that?