Congratulations on taking steps to improve your life Gem. It is kind of common for people, especially women, to develop crushes on their therapists because the therapist actually listens to them. But you must realize that this is what the therapist's job is... to learn about you and figure out ways to help you. Don't mistake it to be more than it is.
Crushes like these can be harmless enough if you don't act on your feelings, but I worry that you will trade one obsession for another Gem. I think that the reason you want to see the women that the men you are obsessed with are married to is because you know that you will compare yourself unfavorably to them. This may sound odd, but I think that in your sub conscience, you want to feel bad because you will have an excuse to "punish" yourself and continue your unhealthy behaviors.
These behavior are crutches for you. Maybe you are afraid to really feel better because you will have no excuse to stay stuck. If you start feeling better, you will have to take responsibility for going to work every day and have no excuse to call in. If you start having self esteem, you may have to start being in a real relationship and not one that is guaranteed to lead nowhere with married men. You are afraid to be in a real relationship I think. I believe that your weight, your phone sex chat, your obsessions with married men stem from one thing: fear.
You may need to find a different therapist and start being treated with medication to control obsessive compulsive behavior.
Again I congratulate you for seeking help which is wonderful, but don't keep seeing this particular therapist just because you have a crush on him. If you are attracted to him and are trying to impress him, it may stop you from telling him any truth that you think is an unattractive one and hinder getting the help you really need.