It is very difficult to maintain self-esteem when someone close to us is hypercritical and verbally abusing. That is what he is doing, you realize?, he is abusing you.

If he were your husband you might be filing for divorce on the grouds on verbal abuse. But just because you gave birth to him, does not mean you have to take his abuse. It sounds like you want to help him, yet you absolutely dread him coming back home. You cannot help him if you are his victim, rather than his mother.

I think you need help for yourself. A therapist could help you sort your self out, help you not buy into what your son is telling you, know yourself and find ways you can regain you self-esteem.