I'm not going to tell my girlfriend that my ex-girlfriend kissed me
Which ex is the one that kissed you?
My ex was my former high school teacher.
You shouldn't cheat on your girlfriend and be dishonest about it. You need to be more faithful and respectful.
It's not cheating, I'm only telling her that I kissed her so that she won't get mad at me. It's not like I want to make out with her.
If your ex came onto you and you completely disliked it, kudos for you for trying to come clean about it with your girlfriend. It may hurt, but honesty hurts less than lying and cheating.