For five years off and on I slept with my best friend's dad more than 20 times. I'm now getting married to someone else and her father is the one who is giving me away.
Have you told your friend that you slept with her father?
No, my friend is very naive about it.
It is not good to sleep with a friend's parent. That is creepy and it will make you seem untrustworthy.
No one is being harmed by this.
No one has been harmed by this yet, but it could hurt your friend if she finds out in the future. I'd keep this to yourself and move on with your life. It's not good to sleep with parents of your friends and you have a new partner to focus on.