I'm feeling heavy BPD emotions right now...which makes me doubt whether I'm being rational or not. 

I'll keep this as short as possible. I had a breakup back in early December after getting into a mutually physical fight. (The ex has tried to project me to everyone afterward as an "abusive" boyfriend although I had never been physical before that and he attacked me first during that night of our breakup...I reacted in self defense to his initial force.) He blew it up on social media...showing pics of the small bruise I gave him, making me seem like the sole bad guy. People have been putting me down since. The cops were called that night and even they didn't do anything because they saw the evidence that he initiated it (how we both weren't arrested is the only fortunate thing in all of it..the cops kind of laughed it off as a gay quarrel). It's been a long few months of remorse, guilt, sadness...and I've been seeing a therapist. By no means has this been an incident thrown under the rug like I have in the past. If anything, I started acknowledging that I have self control issues, whether it's in self defense or not.  The whole moment lead me to where I am now, trying to improve myself and become a better person. I've opened up to my close friends and asked for a sort of support system to get through this emotional stage. My best friend has been one of them that I've confided with...

So, today, I noticed my best friend of 27 years (we are both 31) liked one of the ex's new pics on Facebook. I'm not friends with him on FB, but sometimes get the urge to look...as unhealthy as that is...and some of his pics are visible. I said, "oh you saw [ex's] new pic?' She told me that the ex messaged her and said "hey how are you?"
She said "I'm good, hope you are well."
According to her, he said "If I ever see [mehinanutshell] again, I will beat him up!"..(fitting for someone that accuses others of being "abusive," right?)

I only know details from what she's told me...but at her telling me what he PMed her with, it made me upset. I immediately said, "so what did you say back!?"
I was angry. He's dragged my name in the mud around town since December saying I'm abusive, yet my friend knows I'm not an abusive person. 

She said to him, "Well I'm still your friend no matter how you and [mehinanutshell] feel about each other."

I said to her on the phone, "why would you defend him? He's been hurting me indirectly emotionally these last few months... You know how much damage he's put on me....why would you even acknowledge him?"
She then said, "are you trying to control who I can and cannot talk to?"
I wasn't trying to control her though.  I never said for her to not talk to him, or delete him...or whatever. It's more like an ethical issue in my mind...don't support an ex of your best friend in any means. I would never let anyone talk about beating her up without telling them to "fuck off!" She wouldn't have to be that blunt in words, but to say she wants to be friends with my ex regardless of the fact that it's still sensitive for me, makes it very hurtful. I called her out...
She basically told me in so many words that my emotions and thoughts are uncalled for because I have this disorder (she never directly said it, but it was hinted). It felt like she was just rubbing it in my face that my emotions are "wrong" because she knows I'm borderline...

If anything, I think people here can give me a blunt, honest opinion about how I should feel about this. Am I being too emotional or is this legit something to consider in the scheme of things? So confused...and angry...and sad...yea.