Welcome here to the Forum - and thank you for the trigger warning, it was very thoughtful, a lot of people read these threads.
No, I'm not going to suggest you give up and get a new life, you love him and he his still a very large part of your life.
If he is the sort of person that supports others, something you mentioned, then the constant stress of this will off course take it's toll, and it may be - and I'm guessing here, that the long tern effect has been coping by drugs and withdrawal, needing peace and no constant demands on his own resources.
The fact he may have lied or attempted to drive you off could be part of this.
If he is the sort of person you think then I'd expect he probably might tell you when it's really over -again a guess I'm afraid.
Perhaps rather than just waiting to see what will happen and being worried, maybe afraid, and feeling great loss you might wish to think of things in another way. I realise you have depression, anxiety and BPD, all of which may tend to make you more dependent and life seem horrible, however if you can see waht you can do to be a supporter as well as supported it may put a different flavor on things.
Instead of being another person who will just need help, you might be seen as someone who can offer a shoulder to lean on.
I'm more than aware this is not easy and in all probability a long tern goal, involving , as it has with my illnesses, meds, therapies and time. My apologies if you are already doing this, you don't mention anything other than your diagnosis. This path at least has the virtue of hope.
You did say you had family and friends, is there anyone you can talk frankly with about how you feel - not so that they can try to "fix 'things, but just listen and let you know you are cared for?