What is your definition of cheating?
Cheating in a relationship is any involvment, be it emotional or overtly physical, with a person other then your SO.
This includes, sex, kissing in a not-so-friendly way, groping, long involved talks about feelings, avoiding your SO to be around someone else and the like.
I have been cheated on once. I will not allow it to happen again, if so, the other person is losing something very important to them.
I tend to get a bit worked up on this topic. Hope I didn't come off pyscho.