Hello.

These are just my thoughts:
What about improving your condition for you before making any big relationship decisions? Also, there is no reason why you can not be friends with your ex and still have an intimate relationship with another person. Who says you have to be in a 'relationship' with your ex?

Ultimately, what do you feel will make you happy? Either way your disorder will have to be looked at despite who you are with...In my humble opinion I would recommend working on you and improving your condition first. In my experience with BPD, I had to start taking action with my disorder, otherwise any relationship I have (including friendship) will suffer.

I also recommend posting this in the relationship forum too, there are some very helpful and supportive people there. Best wishes and hope things start looking up for you.