Hi Andy and welcome.
You are not alone with this problem as you can see. I think many of us were feeling fairly worthless by the time we come here or arrive at our first GA meeting. Who would love me when i hated myself? No one thing is going to make things better.
Going to GA meetings helped me. the Serenity prayer helped me deal with the past, ironic really for an athiest/agnostic! The past is one of the things we have to accept we can not change.
In the early days i found that doing small, achievable positive things helped, I hadn’t achieved anything very positive in a long time. Making amends where I could as well.
Mayybe start a thread in the My Journal Forum, keep a track of all your positive achievements. It sounds like you have stopped gambling at the moment? What has helped you do this? What will make it harder for you to go back to it? I look forward to reading the positive steps you are taking.