seriously, am I overreacting????

anon
Gonna make this long story short, my boyfriend who I've been together for almost three years this march has this girl he was, " best friends" all through out middle school and somewhat highschool, let me just be honest and to the point, she was a whore, he told me she would always tell him she wanted to get fucked so bad and have sex constantly.....and he didn't know why she'd always tell him and I told him she obviously was trying to drop hints she wanted to have sex with you... We had this conversation when we first started dating fast forward a year into us dating this bitch comes back again, she wants want to hang out with my boyfriend and this other guy and get high, my boyfriend is not the type of guy to go get stoned.. (not hating on anyone who does) anyways, he told me she really wanted to meet up with him and hang out with him so bad and I was upset and told him i really didn't want him to go that it'd hurt my feelings, he didn't end up going and she disappeared yet again!! Fast forward one last time to tonignt, she requested to follow him on Instagram and he accepted and followed her, idk when this happened because I don't creep on his ig but we were laying in bed together cuddling then he gets on his phone and starts scrolling casually threw his feed when one of her seductive pictures pops up and as soon as he sees it he flies past it so I don't see and I asked him what that was and he said nothing so I scrolled back up to see her half naked, I was furious and said serious this chick again? And he immediately told me I was overreacting and that she just requested to follow him so he accepted and followed her back maybe I'm just a jealous bitch but I need to vent sorry for having this so long, please give me your opinions any at all.
FORGOT TO MENTION, when I first met my boyfriend he told me I looked like her and so did that guy friend I mentioned earlier here our images, I'm worried and don't know what to do, I came from a broken home and have always been hurt so yes I over think things to often, I don't want him to hurt me but he isn't even phased I don't want him in contact with her??