ive been sleeping with my friends baby dad

if you are going to shame me please dont read or comment i know this sounds so bad but here me out, so there is this girl that goes to playgroup i say ‘goes’ she use to come when he was a baby but she has only been once in the past 5/6 months so i would say we’re friends as we speak when we see each other but we’re not close at all. Anyway i got an add from someone a month or two ago, i recognised the name but had no idea where from so i added him back it was only a few days after talking i realised who he was, he was her baby dad. he said he was interested and wanted to get to know me he assumed me they had been split up for a long time but i ignored him for about 2 weeks due it and avoided meeting up, anyway we did eventually have a conversation about the kids and i started to really like him. We then started meeting each other, he would stay over, we slept together a few times, went on dates i really liked him, we did more together in a short period of time than i did with my ex of 3 years. The only problem was we couldnt tell anyone as we knew the back lash i would get from her, her friends and the other mothers from playgroup. she then come back one week and mentioned the fact she knew he had a new girlfriend and wasnt happy about it (not sure why as she cheated on him multiple times and she had a new boyfriend at this point too) without knowing it was me she was really badly talking whoever it was off not even a little like it was BAD to the point it made me uneasy and panic and i knew i really couldnt let this get out. me and him spoke about it and he said he wouldnt tell her but i just couldnt risk it, my son has friends at playgroup and i dont really have any friends other than the parents from there so i couldnt risk losing that and having my son lose out on play dates because of me and my decisions. i then ended it with him which i really didnt want and i made it clear i didnt want this and he blocked me. a week later ive found out they are back together and im terrified hes going to tell her, i know he said he wouldnt but obviously a lots changed since, ive not slept in days worrying about it getting out. i want to message him and ask him to please keep it between us but the only thing i can message him on is facebook and if hes living back with her she’ll have his password so she’ll see it honestly i dont know what to do😩