Yes!! They are "private parts". I hate how technology has made it so much easier to cheat. :(

It's definitely crossed the line. It's sexual activity with another, in my opinion.

Depends on your definition, for me cheating is anything you wouldn't do in front of your spouse. For example, some people consider watching porn to be cheating, my husband and I watch it together sometimes and I know he watches it solo too. It doesn't bother me and actually makes our relationship BETTER because since giving birth and breastfeeding, sex has been physically difficult for me. I love my husband and we're intimate in other ways, but I flat out know he has desires above what I can provide and if watching a video with a bottle of lotion helps with that, I'm happy because I don't feel internal pressure to do more for him than I'm comfortable with (he would absolutely NEVER pressure me, and in fact got very upset when we tried to have sex before I was ready postpartum). Flirting with girls online and sending naked pictures would absolutely be over the line in my opinion and would be a serious breach of my trust.