Hi @Nikolai,
Welcome to Forum Land.
As @CherryBomb mentioned, I have BPD. I am 39 and was diagnosed twenty years ago. Unfortunately, I don't think I have any words of wisdom for you, regarding how to talk about BPD with your partner. I am very socially isolated, and the only romantic relationship I've ever had was with a youth group leader who took a "special interest" in me when I was a young teen.
I've never had any luck at all trying to explain to people what it is like having BPD. I've never found anyone other than mental health professionals who "gets" it (and unfortunately a lot of mental health professionals don't "get" it either!!!!). I am SUPER grateful for the SANE forums because I know there are people here like @CherryBomb who genuinely do understand that the intense emotions associated with BPD are very real and can be SUPER intense.
One of the best descriptions I have heard of BPD is that it's like having the emotional equivalent of full-body severe burns. EVERYTHING hurts. The slightest touch HURTS. This definitely describes my experience. I can go from travelling ok to being on the floor rocking, crying and making weird noises in about three seconds if something triggers my big feelings. It's a pain that floods my brain and takes my breath away.
The thing that helps me most in those times is having someone simply be with me until the feeling passes. I don't have any "friends and family" but I have finally connected with a decent psychologist (loooooong story!!!!) who is able to just sit with me when I get dysregulated in sessions, and I've also called the SANE helpline a few times when something here in Forum Land has triggered a giant feeling, and I've found that they are generally ok with just sitting with me {waves to @Former-Member} until the wave passes.
I think if I had a partner, that is the thing I would want him to know; that the feelings are real, they are BIG and they are incredibly painful. As to how to actually get that message through? I'm sorry to say I'm not so sure.