Should I tell my boyfriend I’ve slept with someone he hates before I met him?

Basically, I met my bf at my new workplace, a few days before I started working there I somehow managed to sleep with the bar manager, and my bf is a bartender. He hates his manager, he often complaints about him to me. I don’t know if I should tell him cause I do want to be open about everything with him but I’m scared he would be disgusted by me for this. What would you do? I really love him.