Fear of losing someone close to you can really take its toll on any relationship. How long have you been going to therapy? It sometimes can take a little while to see progress, but just keep on going...it can only help. While I am not in your situation, I was really afraid of death for awhile, but realized that it will someday and I have to cherish every moment I have. I lost my self identity, became depressed, and was so afraid to die that I would not live...I know it may sound a little cliche, but it is true. Our fears can often overcome our will in some situations.
But I believe you are doing the right thing. Therapy can be a long and arduous process; sometimes you don't realize your making progress when you actually are. Please keep your questions and concerns coming. Also, welcome to this forum; you will find a community here that listens, cares, and can really relate to what you are going through. Please keep us posted.
Therapy is a great start! Don't give up on it! You are doing the write thing!
Sounds to me that you have a fear of loss.
Have you ever experienced loss before? Like a family member or anything?
Keep us in touch, we are here to help. I'd be interested in what your therapist is saying.
You can overcome this fear. =)
God Bless you, and good luck.