cheating between main love interests

Unpopular request but does anyone have any books where MC1 cheats on MC2 and then comes to regret it?

I’d prefer a situation where they really didn’t think MC2 would leave them and then they do and they are grovelling and trying to get them back.

It doesn’t HAVE to be cheating I guess. MC1 could just treat MC2 horribly and take them for granted.

I’d also prefer for MC1 to be self-absorbed and cold and MC2 to be a sunshine character.

Thank you in advance!