I encourage you to continue with your therapy and maybe do some group work if you haven't done that. See if your therapist can suggest a weekend intensive if that would be appropriate for you. Even a week-long retreat where you can just focus on yourself.
I really feel for you.....I know about the intense and heart wrenching fear of losing your lover....your only lover; and how it seems that you will actually lose yourself in the process. And you would lose part of yourself if you lost him.....so the thing I would suggest is to spend time developing, and nurturing a part of yourself which is just for you.....a part of yourself which doesn't depend on anyone else. I have a part of myself that is just for me and that's where I go for comfort when I'm scared.
The key to life is in being fully engaged and peacefully detached simultaneously and authentically in each moment.