How to deal with guilt and regretful thoughts?

Guilt: It is important to uncover the origin of your guilt and also obtain help understanding whether or not your behavior actually merits feelings of guilt. Repetitive feelings of guilt are often caused by being raised in an environment where people held you responsible for situations that may have been out of your control. Best.

Shame: Shame is just about the darkest emotion people can face. It presupposes that there's an audience to our alleged wrongdoings, and that devastating judgement will be passed. Something to remember is that everyone has something they feel ashamed about; it's inescapable. Find a reputable psychotherapist to speak with. Getting it off one's chest in a safe, nonjudgmental place is the first step.

See answer: There is a difference between guilt and regret. Guilt means you should have known better. Regret means your sorry the way things turned out but you did the best you knew how at the moment. It means taking responsibility for your actions, but not necessarily feeling guilty...because you are an imperfect human being(as we all are). Go to the CBT checklist "overcoming anxiety and stress"