Should I tell him

My ex and I broke up a couple of months ago and I slept with someone else. He told me that if I was to sleep with someone else while we’re broken up he’ll never be able to get back with me. I never thought that we was going to get back together but here we are 5 months later working on getting back together. Should I tell him? I told him that he can have sexual intercourse with whom ever once he did it outside of our relationship. Plus my ex was the only person that I’ve ever slept with. Can I get some advice please?