I think it’s up to you to redefine success. Many people define success as graduation, college, and typical social milestones. If you can remind yourself that success is someone finding happiness, safety and security and the other things that your son has found, this situation will resolve itself. The problem is really your own perspective, not anything he has or has not done. For your whole life, you have accepted messages about what success is and is not so now you will have to put in the same amount of time to tear down those myths. Talk to a counselor if you think you need extra support. Every time a negative thought about his life pops up in your mind, challenge it. Mantras can be very powerful things!
Also, give yourself the time to work through this. We’re all humans with our own weaknesses. You aren’t a bad person to be struggling with this. You are on the right path to be recognizing this as a problem.