Help my best friend with borderline personality disorder

I know he is your best friend but I used to have BPD and I had a brother with it who eventually became so violent he would take his violence out on me then he took his own life.

The sad fact you have to face is he is very reactive and it's not going to be a happy relationship for you. He wants you to run after him. I know this. I've done these things. I've had to unlearn these behaviors. Men with BPD can get very scary when set off. They can be prone to violence. Even if they are not, they know how to manipulate and will change mentalities at the flip of a switch if they don't get what they want or feel like they have been slighted.

Please don't get your emotions entangled in someone who flies off the handle like that. It will likely get worse, not better, if he isn't self-aware or committed to change.

Also, in response to him not replying to you: he will come back if you don't. He is probably testing whether you will run after him first, either because he is so scared that you are only pretending to like him, or because he knows that this will end badly and that it will be his fault, and he prefers to ruin it 'while the going's good', in a way that he can control. If you have had BPD or heard someone talk about it, you probably know what I mean.

Also, if he can make you feel like you 'owe' him something for offending him, he might think that your sense of culpability will make you more sensitive to his emotions and wants. He probably feels like 'the bad guy' and 'the loser' all the time, so if you're the 'bad guy' instead for once, at least in his head it relieves him of that role.

Don't run after him and don't let him come back. If he walks off, he walks off.

I know BPD is (mostly) out of his control, but if he has such an explosive reaction over a question about his beard, that's a red flag

While you shouldn't have bothered him over his facial hair, let's be real here: people like him who fly off the handle over little things like that are dangerous and ain't worth shit. Don't contact him. If he contacts you, ignore it.

My advice as a former BPD person: distance yourself from him. He will probably do everything in his power to stop you doing that - including perhaps some underhand or disturbing things, because losing such an important source of intimacy will feel like death to him and it's the one thing he craves, with the desperation of a crack addict - but you're being cruel to be kind.

He isn't a healthy person yet, and although the last thing he probably wants to do is hurt you, he will most probably end up doing so. The more intimate this friendship gets, the worse you are going to get hurt (and the worse he is going to get hurt, too). As emotional pain goes, people with BPD could be said to be 'gluttons for punishment'. BPD can be managed, but it sounds like your guy friend is not managing it right now and that makes a relationship (or even a close friendship) with him an emotional health hazard.

Now re the relationship thing. BPD sexuality is weird. I would be so thirsty for closeness I didn't mind how it came to me. I would obsess so much over platonic same-sex friends that the idea of sleeping with them wasn't unattractive, even though I hadn't thought of myself and wouldn't have defined myself as any shade of 'gay'. He may well do nice things for you and be affectionate, but that doesn't mean you're automatically in a relationship, or that you should be. In your post you sound like you think you 'owe' him more intimacy. He might well think you do, because people with BPD don't have a well-developed sense of relationship boundaries beyond the obvious things like 'don't steal other people's stuff'. Don't be flattered by the fact that he's trying and feel like you have to 'honour' the effort 'or he'll be upset'. If he threatens to break up the friendship, let the friendship go. People with BPD make threats like that and then come running back when they see that you're not running after them: they are that paranoid about whether you have secretly given up on them that they 'check' just to see if you'll run after them. If you quit while you're ahead, you will be doing the both of you a favour. He won't see it that way except in hindsight - until he finds someone else to idolise he will want you back with every fibre of his body.

People with BPD want all the intimacy they can get - they're starving for it, precisely because the way their emotional wiring works eventually destroys whatever meaningful relationships they manage to form and usually damages the person they loved, and pushes that person away. It happens systematically with almost every meaningful friendship or relationship they have ever had in their life. Almost everyone they love, they either lose, or believe they have lost, or are assured that they will lose.

I speak as someone with BPD symptoms who is managing them. I used to qualify for the diagnosis (5 DSM-V symptoms) but now I don't. I know the intimacy starvation and I have a long list of friendships that got very intense very quickly and then went south. After four years of therapy and a vote of confidence from my therapist, I am just about ready to start thinking about dating for the first time since I was 22, 10 years later (self-imposed: I was fed up of hurting people and of getting hurt every single time.). These past 2 years I have also managed to form close friendships that didn't go bad, which I found difficult before.

My ex was as far as I know never diagnosed with BPD but something similar that gives you very similar traits and mood swings. Sometimes I think he may have been misdiagnosed.
He is an amazing man and I will always think so but the sudden mood swings are nothing to take lightly. It's why I would never in my life go back even though he's tried to get me back at times because we were very close and best friends.
He can get pissed over nothing, just say the wrong thing at the wrong time or ask a question he doesn't like and he can't respond normally but goes into rage instead with hurling insults and making a big deal about it and there is no way to communicate maturely with someone who blows everything out of proportion. Not always like that but it depended on his current mental state and how stable he was at the time which varied and went in waves. It drives you mad in the long run to deal with someone who may be great but who keeps crashing into mental instability and taking it out on you because you're the closest person to him. It's not worth it in my opinion. That said yeah a person with BPD can be cured even but they need to actively want, seek out and stick with the treatment offered to them and all too often, as it was with my ex, they quit treatment after a while due to thinking they will magically get well on their own. It entirely depends on each individual but this guy of yours obviously has some problem controlling his anger. It's one thing to get annoyed at someone making a remark about something like that but another to go completely apeshit over it and ignore your calls for days.