Is it cheating if your boyfriend/girlfriend kisses another guy/girl for fun once?

Anonymous
So me and my boyfriend were discussing this today because he did that last weekend. I wasn't bothered at all about this. He's a straight male 100%, comfortable in his masculinity and has no attraction whatsoever to guys, just to let you know. He and his friend kissed as a fun thing just to joke about the fact that us girls can kiss on the mouth (like hello/goodbye) without it being seen as gay.

I'm against cheating 110% just from seeing it up close so many times and I'm disgusted by it from the bottom of my heart. But this I honestly just found amusing but it made me think, is there anyone that thinks that it's cheating if your boyfriend/girlfriend kissed another guy/girl just for fun no matter what?
Updates
+1 y
Realise the question could come off as wrong but I mean if you're significant other kissed someone of the same sex. Not like '' Boyfriend kissing a girl'' for fun :)
Is it cheating if your boyfriend/girlfriend kisses another guy/girl for fun once?
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