My friend slept with my boys dad while we was together still back in 2017

My friend just told me her and my boys dad slept together back in 2017 while we was still together right before I got pregnant with our second we was friends at the time she came and seen me at the hospital when I had my second child. Apparently he told her he was single only had 1 kid they ended flirting with each other and slept together I don’t see how she didn’t know we was in a relationship status on Facebook we have been since we been together. She waited 3 years to tell me but me and my boys dad haven’t been together for a couple months tho it’s the fact it happened while we was together and she waited 3 years to tell me should I just drop being friends with her period ??