You don't know he will be happy ever after though. It's important that you work on yourself and the things that made you vulnerable to getting caught in his trap to begin with. You are probably an nice person and are vulnerable to this kind of individual who depends on that for "their" own narcissistic feed. He did the drinking and driving and cheating because he is "selfish" and only thinks about what "he" needs. He will probably do the same to his next partner too, feel sorry for her.

You deserve to work on your depression and feeling so low you have bad thoughts. This is a common challenge for those who were swept off their feet by a narcissist who at one time made them feel they were so important and appreciated only to drop them for selfish reasons that have nothing to do with their true value as a person.