In my current relationship, it would be cheating. In the past, that wasn't the case.
I should expand upon this.
My dude and I are long distance and always have been. We have one more year apart to get through before we can be together. We met online in a game. He was looking for me. I wasn't looking, but when I see a gem I don't leave it on the table for someone else just because I don't have a setting prepared. Our first sexually charged interactions were not like similar experiences I had in the past. We were as nervous as we were insatiable. When we couldn't get off anymore, we'd fall asleep, still connected to Skype or on the phone. At first that wasn't deliberate. It was past bedtime, and we were trying to stay awake but just passed out. We never wanted to disconnect. Now, we deliberately go to sleep on the phone together. We say our good nights, remove headsets, employ speaker phone, blow kisses, and go to sleep. If one of us wakes up and doesn't hear the other snoring or breathing, it upsets the waking party. Our primary sexual interaction is still by phone or cam. We only meet a few times a year. I was supposed to be at his home this last weekend, but couldn't go. We haven't seen each other since December. If one of is used camming with someone else as an outlet, it would be a huge problem for the other one. First of all, we haven't made time to cam in ages. We haven't had phone fun in a while either. What message would it send to then be making time to do that with an outsider? Since it is our primary way to connect intimately, making similar connections, even lacking any emotional component, would demean what we do together. Not acceptable at all.
As for flirting, well. We're both attractive, and we're both huge flirts. I wouldn't want him flirting with someone he knows well in person, but I've heard him getting flirty with cashiers while I'm on hold on the phone. Doesn't bother me. I know he flirts with women online, and that doesn't bother me either. He doesn't try to hide it. I know some of them have gotten angry with him after he tells them about me. That's their issue. I'm only upset if there's no cheeky talk left over for me. I flirt all the time. I don't hide it. Some folks here can tell you I'm not flirty in private messages, no matter what is said to me, but I'll flirt with those same folks where it is publicly visible. I never want my dude, who is a silent but regular member here, to be able to say I was ever deceitful, and I'd like him to be able to tell me if he thinks my manner is crossing a boundary. I love and respect him, and what we are building together. It has been a long time since I looked at a man and wanted him to impregnate me. I want us to be family, and for him to always be able to respect me as his life partner. I moderate my behavior accordingly, and I expect him to do the same.