"and this is where it gets downright traumatizing..."

I know... I know.

"The rest? not once did they even bother to attempt to be there for me, not even after all the times I've been there for them!"

Maybe they are afraid of your episodes. I know my relatives are. Our expectations are very important to our survival. What is the reason of being there for them, that they might do the same for you? If that is the reason, deep down sub consciously, then you are putting yourself up for disappointment. You do it because you are human, not expecting any rewards and in your journey, life will reward you as a side effect. Then it will be health to your soul.

"The only one who tried to be there, was my ex, and we are currently trying to rebuild our friendship and I'm not comfortable reaching out to him because my drama hurt him badly last time (bp/bpd episode)"

Be very clear of your expectations for him. Make sure you only expect those he can do in practical living. Talk with him if you are not sure. Be considerate to him at all times not expecting a reward from him or that he do the same for you. You do it because that is who you are. Everyone has their own strength and weaknesses. Try to communicate slowly, don't overwhelm him with too much info. Normal people can't take it. They walk away.

You don't have open up yourself to him if you are not comfortable. Just be yourself. Do one thing at a time. Tackle one issue at a time. Get one need met at a time. Take it easy but take it. Be patience. Certain things take time to see results.