I think you nailed it there in your description about him having put you in a silo in terms of just being there to offer support and then he leaves again once he feels better. That's a pretty powerful realisation.

And it's definitely not a true friendship either – imagine if one of your actual friends treated you that way? Came running when they were down and asking for your time and energy, but refused to engage beyond that, and blocked you every now and then when they felt like it. We simply wouldn't tolerate that from our friends.

It's helpful I think to remember that what someone with BPD is actually looking for is the perfect parent - they are trying to solve or soothe something from their childhood, and their relationships are dependent on someone else meeting the needs of this immature, wounded, underdeveloped part of their brain. It doesn't actually matter what your needs are, as long as you are fulfilling this role. So no, that's not the true definition of a mature romantic love, or anywhere close to it.

Aside from the fact that it feels good to you to be able to support and help, he's not actually meeting your needs at all, so I'm glad that you're seeing it through this lens, as painful as that is.

Sometimes we have to see things from different angles in order for them to settle into us properly... we can know all the things logically and still not be ready to integrate it and accept it and truly leave it behind...

I've been through a similar realisation with my just in the last week. I'll maybe post on it separately another time, but I had the same lightning bolt... he simply didn't and doesn't love me in the same way I loved him. Even though he was the one proclaiming all the amazing things about love forever, soulmates, and never letting me go, he was simply trying to stop himself from being alone. His love for me was never about me. It hurts a lot, I really do get it... to be unseen and used for what you give rather than who you are... that's not love.

Even if he does have some realisations in the coming weeks or months, which might potentially happen if he is on his own, and you're now seemingly leaving him as well... so be prepared?? But even if he did have all the realisations, the question is does he have the emotional maturity or skills to ever have a relationship where you are appreciated for who you are? And there is reciprocity and interdependence? If you try and project beyond the here and now, which is a painful game of cat and mouse... being in a relationship with someone with BPD traits is most likely going to be a painful and exhausting, and one where your need are unlikely to be important.

I don't know what the dynamics are between you, but Karpman triangle dynamics helped me to understand what was incomprehensible behavior on the part of my BPD mother when my father was ill.

BPD mother ( and I think this applies to most with BPD) takes victim perspective. My father's main role was rescuer/enabler. His being ill decreased his caretaking behaviors- and with this shift in dynamics, BPD mother's behaviors escalated.

His being ill was a form of temporary "victim". It surely wasn't his choice or fault, he wasn't doing it on purpose, but from BPD mother's perspective- she was in victim mode and so, other people could only be rescuer or persecutor. It was as if she perceived him as some kind of competition for her position and if he did it on purpose. I also wonder if she felt somehow abandoned in this situation since he wasn't as attentive to her as usual.

You could apply this to your situation. You asked your H to pick up your medicine, but he's tired and his being tired is him being in victim position. You are supposed to be caring for him, not the other way around.

You have every right to your feelings and to be angry. I hope this helps you to see his behavior isn't personal to you. But also to see that he may not be someone you can rely on if you are feeling under the weather. I hope you feel better soon-

The general observation here is that over time the poor behaviors (cycling, rants, rages, criticisms, etc) gradually increase over time.  It still cycles between less bad and more bad, but over time it typically worsens.

That's why my marriage ended.  (Well, there was a big trigger too, we had a baby and that changed everything, including morphing me from seen as a husband to seen as a father.  Too bad her stepfather had messed her up badly.)  We started out fine, with 'only' minor issues but over the years it gradually got worse.  More and more triggers developed.  Adding the baby was a nice try but was too much for her.  Sometimes it seemed she had to choose between our child or me... and I lost.

I hate that things ended so abruptly - that I blocked him and then he blocked me. I want to write him a handwritten letter to let him know what he meant to me, that I love him like a friend, and that I accept he isn't right for me romantically. I don't want him to feel I abandoned him. I don't expect a reply.
Is this a bad idea? Should I just leave the parting as it was - uncomfortable and abrupt?