I really need some advice so if someone could give me some input I really need it

My ex and I broke up in June or has been extremely hard for me to get over it still, I am still very in love with him. He met someone new and It hurt a lot but me and one of his good friends from high school (it’s our first year of college) started snapping a lot .

My ex and this guy arnt that close anymore

But the guy and I ended up meeting up over break we just watched a movie and did nothing but “cuddle” I honestly don’t know why I did it. I regret it. And I’m afraid if there is a chance my ex and I get back together (which is a high possibility) I’m going to have to tell him. It was kinda fucked up of me to do that even tho I didn’t mean anything by it.