I regret/feel guilty about a great many things and at times it can be quite difficult. It is depressing, obsessive, and causes anxiety. One thing to remember is that decisions in the past were often made with the only information available to you at that time. It is not until later when you are presented with new information that you regret the decision. Which only proves that you made the best possible decision you could at the the time, so there is point in regretting it later. It serves no purpose.

Life is full of wrong decisions and instead of regretting them you should study them and learn from them. You will actually gain confidence about your future this way.