BIG DILEMMA HELP.

I need help cos I genuinely don’t know what to do, deep down I want to tell him but everyone is telling me not too.

I was in a toxic relationship for about a year in a half I wouldn’t say he was terrible but he didn’t speak to me nicely, he broke up with me, we didn’t speak for 3 months and I went about my life I was genuinely happier and I was ok with be single. We started speaking again I don’t even know how it came about and we agreed to meet up as fwb. (Such a stupid silly thing) but I guess you just do naturally have sex with an ex like that.. he made it clear that he basically wanted to have sex but had no intentions of getting back with me I kinda felt weird about this although I agreed it kinda ruined the mood? Anyways we forgot about it and things got left we didn’t sleep with eachother..

I met a new guy he was really nice and we slept together and my ex started speaking to me again I told him I was seeing someone (didn’t say I slept with him) and he completely changed his whole attitude saying he wants to see me, change etc and wants to be with me and loves me, I know an ex is an ex for a reason but I gave him the benefit of the doubt and now it’s eating away at me that I’ve slept with someone else because I just know he will go crazy at me and shout even know I know I’ve done nothing wrong... what should I do? (P.s where I live is a small area, so he would find out eventually)