Having a pure physical relationship

What’s the opinions of guys/girls on being in a physical relationship with someone only just to have fun ,then find out that other person male/female irrelevant, saw someone else on the side because they felt lonely? Would it matter given the lack of seriousness and the fact the relationship was only physical to begin with ? And no it’s not relevant to me it didn’t happen to me.However I’m with the woman who did tell me the story and it was her past ,kind rubbed me the wrong way ? And no I wasn’t the other guy.