I decided to look up cheating in the dictionary to see what it had to say.

The part of the definiton of cheat that applies here is :
Cheat : [Slang] to be sexually unfaithful

I went on to look up unfaithful :

failing to observe the terms of a vow, promise, etc.
faithless and / or disloyal
guilty of adultery; adulterous

If you are being with more than one partner at once you are being unfaithful and therefore cheating (and adulterous)

Sorry, there, I believe that you should stick with one partner at all times ( always been a moral of mine, even when I wasn't religious, now my moral is compunded with my faith )

So, in my opinion -

CHEATING IS NEVER ACCEPTABLE!!!!! UNDER ALL CIRCUMSTANCES!!!!

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Wow... Funny isn't it? How you think Love has finally found you..... But at a whim it withers and blows away...