I think cheating is going behind your s/o's back.

My boyfriend lets me do pretty much anything but if I want to fuck the person, then I need his permission. I'm a bit more strict, he can play but no fucking in anything other than a 3some. When a guy goes down on me or fingers me at a party, we don't consider it cheating ... but I guess I'm a bit of a hypocrite because I really wouldn't want a girl giving him a blow job unless I was there.

Cheating is subjective.