I want to start this off by mentioning that I was never officially diagnosed with BPD, yet I have a lot of symptoms and I'm finding it hard to cope. I just want to vent about an issue that's taking a toll on me, and I know this is a common issue for people with BPD, so I want to post this in a community where people will understand and empathise. 

A few months ago I met someone wonderful. Caring, funny, intelligent, organized, one of the best people I've met in my entire life. We became close really fast and basically for the past few months, we spent more time together than we did apart. I have depression, anxiety, OCD and ADHD and he understands my moods and triggers because he also has mental illness. I admit that we've crossed boundaries and yeah, we had sex, but this did not complicate things. Overall, we both just wanted someone to be close to and intimate with, but I've always seen him as a friend, a really close friend. I'm also his closest friend and I know he'd be extremely heartbroken if I choose to walk away from this. 

Basically, around 3 weeks ago I started to feel detached from him. To me, this was really sudden, and it came like a total shock. I admit that I'd started to feel a bit distant a few days prior but I thought to myself that this is just a temporary thing, but then one day something basically SNAPPED (that's the best way I can describe it) and I started to see him and the relationship from a warped perspective. I went from caring and interested to distant and cold in a matter of days. It got so bad that, at some point, we were in the same room and I had this urge to run away. I started feeling like he's a stranger to me and I kept looking at him and trying to remember who he was and what he meant to me, but all I felt was nothing. To put it short, I suddenly started to see him like a stranger and went completely cold on him for no reason, in the span of a few days. 

I don't know how to cope with this. I care (or at least used to care) a great deal about this. I've wanted this kind of relationship for so long and he's just a wonderful person, I wouldn't want anyone else in my life. He's one of the most loyal people I've ever met, and he's so brutally honest and open with me in a way that he allows himself to be fully vulnerable with me. Breaking things off would literally ruin him and his self esteem because he is incredibly sensitive (in a very sweet and innocent way).

I've been through this with others but it didn't come off as a shock because most of my friendships were casual and didn't mean that much to me in terms of emotions. But this one hurts like hell, because I'm losing one of the best people I've ever met, and there's nothing I can do about it.

Again, I don't know whether this is borderline or not, but I just need some opinions from people with BPD because I lack perspective at this point. How common is this for people with BPD? Also, is it reversible? Can a person with BPD just snap back to caring about someone after going completely cold or is it basically over once it happens?