If you're engaging in some kind of communication or activity with someone of the sex you're romantically/sexually attracted to, and deliberately hiding it from your partner or don't want them to know about it, that's cheating in my book. It doesn't need to be defined with specific behaviors.
I could forgive my boyfriend flirting, I would hate him for texting girls, but I wouldn't open his phone, see the texts and be like "you're cheating on me? How could you?" I would say "ARE you cheating on me?" Meaning that texting is what leads up to cheating, and cheating means sex or kissing
Any behaviour that is intended to gain a sexual encounter, or form a romantic attachment with a person who is not your partner.
Sexual encounters include any skin-to-skin with genitals or breasts, and any insertion even with condoms, gloves, dental dams, etc. If you can contract an STD if you did this without protection, it's a sexual act. It's not cheating if you SO has given consent for you to see or sleep with other people.
Romantic attachments include any attempt to fall in love with, or get them to fall in love with you. Exchange of vows of love or promises to be together in the future, or plans to leave current SO for this person.
Porn and harmless casual flirting, including "smack ass" and breast grabs aren't cheating if you don't intend to get physical, and the person you're flirting with knows this.
Almost all of those. Harmless flirting is fine, I guess. A bit rude but whatever, it happens. But I consider kissing, verbally talking (phone sex), electronically talking (cyber sex), and actual sexual relations cheating. Having fantasies is one thing, acting on them is a betrayal and I wouldn't trust my partner again.
Kissing and beyond is cheating So is emotional cheating , such as liking someone else
I think all the things you listed are cheating, you are attempting to create a relationship of a sexual nature (fantasy or otherwise) with another person. Any behavior you wouldn't want them to know about would also be cheating, which is why one should live there life in a manner where they can live with everything they have done and be perfectly comfortable with others finding out about it because they frequently do.
Cheating counts as anything your partner do to another person. For instance, kissing, sex, affair, etc, talking to someone in a nonsexual or sexual way. Even when they say they were "drunk" and they did this to someone. In my perspective, even if you're drunk, you still got a conscious mind, well more like impaired but it doesn't make you stupid! If you want it, you want it, if you didn't want it, you could've stopped it. As easy as that.
None of the above really. I can be in an open relationship, I don't mind that. Cheating is lying to me. I don't give a shit about sleeping around, just keeps my doors open too for if an opportunity arises, but lying I will not abide.
Your update, is still cheating. If you do anything with another person, it's cheating. And despicable.