As someone who's got some experience with BPD (my Mother has it) I can only express how awesome you are and how lucky your Fiancé is to have you. Its not an easy thing to deal with.

For you: I would try to find a way to avoid the things that are triggering your BPD. Seems like your environment is a cause. (but you prob. know this).

Things like stress, anxiety, messing with your phone w/o a blue light can distort your sleep cycle which will have a snowball effect.

Same thing for alcohol, weed, and other things that will disrupt your hormones.

For him: we Men are simple creatures and we don't need much. Like you said, you at a certain angle is enough to get him worked up. Keep doing the little things .. they matter tons. Sex is all fine, but you aren't 100% .. it wont mean anything.

Stay awesome. Hope you get better fast. So you and he can show that bed who's boss.