I've felt like this for so long and so many times in between.

Therapy does help you though. It helps you to realize that maybe everything that you think is your fault and that you've ruined, that it wasn't your fault or you weren't entirely to blame. If you were, a therapist can help you work past that guilt and shame and you can try to accept what has happened.

It also sounds like, maybe, you need someone to care about you even if you are feeling like a 'toxic mess' or a destroyer. A therapist can be that source of support and compassion --- even at times when you feel you deserve none of it.