Buddy, I hate to break it to you, but joining a gym, reading group, making music is not going to do anything, it's not going to do ****. Nothing is ever going to change, until you stop beating yourself up.
Girls can sense that a mile off. They can sense desperation and self-revulsion better than anything.
You're going to have to reprogram how you think of yourself- the brain is nothing more than habits and patterns. It's simply a matter of changing or "re-wiring" those patterns.
When you start accepting yourself, liking yourself for who you are, that's when you'll see and feel change.