Am I a bad person?😩

Sooo about a month ago I slept with a guy I've been talking to for awhile. I've been single for quite some time.. I went through the normal questions like are you single. His answer was of course yes.. I recently found out he's in a relationship and he has been for 7 years!!!😭 I feel horrible. I feel nasty. I want to tell her but I know she'll hate me for it but will continue to be okay with her boyfriend and I'm not a drama person but oml I feel terrible 😴