Thank you for writing. I can understand your boyfriend’s worry and frustration that you can’t seem to enjoy life. But I don’t understand his accusations that you are cheating. That sends up a big red flag. It suggests that he is insecure and controlling. You don’t deserve to be defending yourself. Do consider whether you are so grateful to have someone in your life that you are accepting unacceptable behavior. If he keeps this up, he’s not for you.
On your side: It does seem that you are too dependent on your boyfriend for your emotional well-being. He cannot and should not be expected to be your only anchor. One thing I know for sure (and there are very few things I know for sure) is that the less a person does, the less they feel able to do. If you wait until you are motivated, nothing will change. I suggest you make a list of small steps you can take each day to make life happier and work on doing them — even if you don’t feel like it. The more you do, the better you will feel about yourself.
You mentioned medication you are taking but you didn’t mention whether you have also participated in therapy. The treatment of choice for symptoms like yours is a combination of therapy and medication.
If you haven’t already been in touch with the Body Dysmorphia Clinic at Mass General Hospital in Boston, I hope you will contact them. Focused treatment on that issue might help you with your other problems as well.
I wish you well.