Yep they both did it with others contrary to their promises. But they acknowledged that it was just a juvenile and immature promise in the first place while talking about it. After revealing it to each other, it was not mentioned anymore in the story. This is practically a clean slate, a new beginning for them, very realistic
I think ml already said it. When mc asked him, "Did you keep the promise of keeping your pants on?" And he replied with "I... didn't". Then he went on about he didn't care if MC didn't keep his pants on either, he didn't care if MC had a relation with that guy with a car, he just wants to win him over again.

When does ml reveal that both of them did dated around, not just the mc?