Well first I would like to tell you to stop telling yourself that you do not have much to offer people. I am sure that you do, but you just have to harness the energy and find out what that is and stop being so down on yourself. I think that a large part of your problem is that you beat up on yourself a lot. No one in this world is perfect and we all have our downfalls. But you cannot let those down falls over shadow the positive things that you have going for yourself.
Some positives that I see in just reading this is that you seem to be very in tuned with yourself and what is going on with you. I see that you are receiving counseling for your depression and I think that it great. Sometimes a life coach can be good to. It is different from counseling in the sense that it helps you create a plan for your life so that you can feel like you have a purpose. I think that this is what you need. Even if you do not get a life coach. But write down a plan on what you want to do. Even if it does not seem attainable, write it down. then write things that you feel you can do now to bring you closer to that goal. begin to write the good things about yourself and the good traits about yourself and repeat then to yourself everyday. This will start changing the way you think about yourself.
You said that you have low self esteem. When you said bad things about yourself, you must erase them from your mind and make an effort not to say bad things about yourself. The point of this is to retrain your mind on how you look at yourself If you tell yourself everyday that you have low self esteem and that you are a coward, then this is going to bring you lower and make you feel worse everyday. The key to getting your girlfriend back, is to because confidence. The male in the relationship is suppose to have these traits, and you can have these trait, but you have to start believing it yourself. Find a purpose on your life, find out what you want to do, and then make small steps everyday to get there.
I am sure that once you find your confidence then you will feel more secure in your relationship. You will know that you will be able to withstand the trails. After all, what you are going trough is a trail....but yet you are still here and you are still trying to get yourself together. That in itself take strength. You have to start giving yourself credit for that. Once you begin to believe in yourself, you will see that the counseling and medication will work better, because it is a combined effort, and you are not just relaying on the mediation to fix you. But you are putting in equal amounts of work to fix yourself.