Hi Kittycatforever-
And welcome! I'm sorry you're going through that, it's very hurtful and confusing, although not rare around here, we've all been there and we understand.
I feel crazy. Did I miss something? Can someone's feelings change in a week? Why? Why doesn't it happen in person?
Borderlines lack what's called object constancy, meaning when someone isn't with them physically they have trouble connecting the emotions they've felt for the person when they're with them when they're not. Kind of an out of sight out of mind thing, but more out of sight out of heart, and it's not voluntary, a borderline just lacks the ability; my ex knew that about herself on some level, so she asked that I leave her a dirty t-shirt or whatever, and the smell and the physical object helped her connect, although it took effort.
And the other piece is fear of abandonment, the core of the disorder, and you not answering his call could have triggered that, regardless of the actual details of what happened.
So you mention you feel crazy, which is totally understandable, what else is going on for you? Telling us can be cathartic, as you grieve the loss of the relationship, process the emotions and detach.