You have done something wrong in your past and now you are not able to forget this because of this you hate yourself and keep unhappy you want to regret for that How can you do it you dont understand?

Regret prevents the lesson. We are born to live and reach out and make relationships (intimate and otherwise) and test the waters. Everyone makes mistakes. Some are tragic, some are small. Remember that you want to learn from this and try to look ahead. You should also rule out any clinical depression as a result of your previous actions. It is very difficult to move forward if the chemicals in your brain wont let you feel like yourself. Small goals turn into big steps. You will learn to love yourself and grow. And that's what it's all about!