how difficult it must be to not know where you stand, and to not have any answers

i hope that as you go through this, you can find support here.
its a rock and a hard place, for sure. it is definitely best not to push; it is, in general, but with someone self isolating, it can push them away further.
mental health struggles are sort of a norm for someone with bpd. self isolating and needing space isnt uncommon. at the same time, being back on his medication, and focusing again on recovery may be a really significant life change for him, bigger than it might seem to you or me, and it can bring up a lot of complicated feelings.
that, in turn, can be especially hurtful to loved ones, and its a pretty difficult place for you to be, obviously.
is the relationship worth pursuing?
that, ultimately, is a question only you can answer. we can support you and inform you as you grapple with it. its not easy to love someone with bpd, and "stay or go" is an intensely personal, complicated decision.
has he ever done anything like this before?