I slept with my son's father after we had broken up, knowing he had a girlfriend.
Why did you sleep with him even though he had a girlfriend?
I wanted to make his girlfriend jealous.
It may be a better idea down the line to only sleep with people who are single. This will keep you both out of trouble.
I got what I wanted, so I don't care if he's happy or not.
Try to be more empathetic in the future. If you only worry about you want you are going to have trouble making any lasting relationships in your life.