Previously engaged...

I've been seeing this guy for a few months now. And I keep thinking about if I should tell him I was engaged about a year and a half ago. Me and the guy at the time knew each other for a long time. But never dated. Dated and then jumped into that. I called it off after a month. But idk if I should act like it didn't happen. Or... I don't want him to get upset but I don't want to keep it from him.. I'm so torn.