So I am painted black.
[snip]
It's like he's actively avoiding me giving his own stuff back to him. Why? It's his! I don't want to be reminded of how much I love him and how much he hates me every time I look at it. I don't know what to do.
Hi Littleopener,
This sounds very frustrating. Unfortunately, eventually, relating to a BPD almost always (always) ends up frustrating. But there are things you can do to reduce it, and perhaps make it go away completely (the frustration).
I read through your other posts to get some idea of the background. It appears to me that he might be having the same reaction to the stuff that you are. In other words, he doesn't want to be reminded of something, some emotion, by contacting you in any way. That's a common thing to happen in BPD splitting.
The difference between how it's happening to you and how it's happening to him is that yours has a logical and rational cause, his doesn't. His is happening because his BPD triggers his negative emotions too fast, too often. He's been like this all his life and it probably scares the sh-t out of him, and so he avoids it. So if I'm right, then in a sense you're both in the same quandary over the stuff -- although the causes are different. But the end emotional result is the same.
So that might answer your 'why' question for him. It's because he has BPD, which is a mental disorder, and causes his emotions to flare too strongly and apparently irrationally. And causes Splitting (painting black) as well, which you already know about.
All I can suggest is that you do some more reading, and thinking, and breathing, and start getting comfortable with the fact that he's like this and probably will be forever.
That might help you decide whether to move on to the Leaving Board or the Staying Board -- although I'm having a hard time imagining you on the Staying board, considering how clear he is that it's over.
About the stuff itself... .I understand that having it is making it harder for you to move on. Could you store it at a friend's place, and then if he ever asks for it he can get it from there? Or, if it's not worth too much, give it to the Salvation Army? It sounds funny, but seriously, he doesn't seem to want it, and you don't want it. Maybe somebody there can use it.

PP