You should agree with your partner on the very beginning of your relationship what is cheating for you. I'm not in an open relationship, but I won't make a big deal if my GF kisses one random guy in a club one day (and vice versa.) But we won't tolerate lies, other lovers, etc.. If it's casual, it's ok. The big stuff, no!
But make it clear from the beginning.. It will save you lots of problems later!
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