My partner cheated on me twice but I’m still with him but don’t have the courage to leave him why?

You still see that person as the person you met him as. I'm sure you began dating him because he was good for you. His actions show otherwise now. It's hard accepting someone has changed or they are not good for you anymore because you still have a memory of who they were when you first met them. You created a bond with him and shared so much together and you still hold that close to your heart and there is a fear of letting him and those memories and connection go. It's hard to do but it has to be done.