SOO ANNOYED;;need to rant

Basically a few months ago I had this boyfriend who's a complete dick head but I was inlove with him. My friend (that posts pictures of her nearly fully naked on the Internet) use to insanely flirt with him and I found out she use to like him. She's the sort of girl that likes male attention even when they had girlfriends AND she's got a boyfriend herself. So today I couldn't go out with my group of friends and new boyfriend (we've been together about 11/2 month)  and I get snapchat videos and such of her being 'close' to him. I don't trust her one bit with my boyfriends and it's annoyed me so much I burst into tears after watching the videos. SOMEONE PLEASE HELP ME! I also overthink a lot and have depression which means my mind is my worst enemy basically but yeh please help me