I agree with you.
mo·nog·a·my/məˈnägəmē/
Noun:
The practice or state of being married to one person at a time.
The practice or state of having a sexual relationship with only one partner.
Kissing, flirting, anything like that, to me is sexual, and therefore breaking monogamy. But its different for everyone.
Yes, I think this debate should probably be only for monogamy relationships, because in polygamy, obviously people who are in relationships with multiple people isn't cheating since they all agree to it.
But kissing on the lips IMO is a sexual act, actually it's quite defined as being a sexual act, even just a kiss with no tongue.
I believe there's more forms of cheating than just simply having intercourse. To me, kissing, flirting, ANY form of sex, oral, intercourse, touching sexually are all forms of cheating. Some people may not define those as cheating, but all those things will lead to sex eventually (and if it doesn't, you know you're having a thought of sex when you flirt with someone. People can't lie on that.)
And then there's the people who deny that they are cheating while doing things other than having intercourse, just basically someone trying to bend the rules in their relationship without their partner knowing.