PLEASE TELL ME IM GOING CRAZY.

Can someone please tell me if I'm going crazy?
So my boyfriend has this best friend he's known for a while and they use to be lil manwhores and fuck around with all these girls and i told him that I don't mind that when we got together as long as I'm the only one during our relationship. It's been a great 2 years and he's kept to his words
HERES THE FREAKIN PROBLEM.
His best friend always try's to instigate bad shit, like sending him pictures of his ex-gfs who are basically nude. Telling him to go out like they use to blah blah blah.. anyway he sent him a video of him having sex with this chick and I saw it in my boyfriends deleted photo and was panicking because it looked like my bf, soon to find out it's not.  Anyway he deleted the video from his friends messages and lied about it and doesn't get how screwed up it is that his "friend" is sending him crap like this, and doesn't tell him anything. And I'm just here like wtf do I do. My bf says "it's not a big deal he's my best friend" 
TELL ME HOW TO FIX THIS.