No one is immune to their demons. I had such thoughts even after becoming an accomplished martial artist and US Marine. I didn't quit. I told myself "You want to feel better? Be better? You can't do those as a dead man." I told myself again. And again. And again. I highly encourage you to listen to the very last broadcast of Tom Leykis. A lot of people think he's a POS, but he's got a heart. It's there. His general message is you have to tell yourself "I'm better than this. And if you don't believe it, you must become better than this."
The later part in his broadcast, he stated something I hear my own mind echoing. "No one told me how good it would all be. No one could." I find myself honestly living life in a way I wish every man could. They won't though. Unfortunately some give up.
I know you are capable of doing more than even you believe you can with 100% conviction. It's up to you. Why am I so convinced you can? Because I know men who accomplished a lot in life, were bad a$$ 'hard charging' men and they're under our feet. I recommend a couple of songs that helped me to shake the tears loose and move along. Randy Travis "Out of My Bones" and Seventh day Slumber "I know." For that second one, ignore or don't ignore the religious connotations. It's still powerful.