“Best Friends”

I AM LIVID LADIES. So my boyfriend has a best friend he’s known for years and she is a female and I have no problem with her just to clear up it’s not the fact it’s another female in my current situation and, a month before me and my man got together he became friends with this other girl and started calling her “best friend”. So I looked through their conversation from before we got together when he was “best friends” with this girl, and yes ladies he was standing there as I did it because I asked him, and there was messages of him talking about grabbing her booty and how they messed with each other for at least a month. Now when I found this out like last month I couldn’t be too mad because it was before we got together so I brushed it off and they didn’t seem to talk anymore since then. He kept saying she was a bitch and all this, well today she posted a picture of him and caption was “best frannnn❤️”. AFTER NOT TALKING FOR ALMOST A MONTH. So I just wanted to rant and know y’all opinions because I am LIVID right now and I don’t know if I can trust him and that girl since they are “best friends” again. What if they start doing stuff again while with me this time? There are some sneaky hoes out there.