Ok so I'll go straight to the point. I was feeling really shit these last weeks and I always went to my boyfriend for support, until he was feeling bad mentally and needed his space, which I respect. The thing is, he almost didn't talk to me, and that's completely fine because he needs space when he feels low, but I saw on Instagram that his best friend was going to his house. I had a fucking panick attack because I was already feeling extremely paranoid that he was talking with everyone but me, that he needed distance but only from me. That was like a confirmation and I panicked. I told him I was feeling horrible and wanted to talk about it because relationships don't work without comunication, and he told me the truth of his situation and that he wasn't talking behind my back, that day he was feeling better and they talked to him because they needed to do their homework in his pc. I calmed down and tried to rationalize, the extreme physical pain I was feeling because of my intense emotions vanished and felt much better.
Later that night I woke up at 6am and saw that his bestie uploaded an Instagram story. She was sitting on top of him, they weren't cuddling or anything but still, it's kinda weird and felt bad about it but tried to no think about it and sleep for a little bit more. I had a nightmare about him liking them more than me (won't go into details it's long af), and now, the next day I told him about my nightmare and my jealousy and he said he will be more careful and not upload that kinda things. Completely fine I guess but in which world you decide just after hearing your partner having a breakdown and talking about their jealousy, that you're gonna upload a weird story about just what bothers me? I always try to make him comfortable and be better for him but, does he even care? I told him many times that his friend makes me jealous, but ehy would yo keep posting weird shit online, even knowing it will probably bother me? 
I don't want him to stop hanging out with them, I don't want to be a toxic person, what else can I do? I think anyone without bpd would feel like shit if this happened to them, it's not my fault really. I found it really disrespectful, it's like they are the couple and I'm his friend, I don't know what to tell him anymore without sounding controlling or toxic or manipulative or shitty.