i need help

so i’m starting to feel guilty about something i did.

me and this girl USED to be friends a couple months ago. then all of a sudden we wasn’t anymore, didn’t talk or nothing. well me and my baby daddy broke up and i was kinda vulnerable and hurting so i started texting her ex.. just for attention i guess didn’t think nothing would happen, then we had sex.... multiple times and he started to actually like me, and i was sorta feeling the same way. well for two weeks now me and the girl have been talking again, and hanging out. should i tell her about me and her ex or keep it a secret as long as possible? I have terrible anxiety and I overthink everything so this is becoming very hard for me.