What is cheating? - Give us your definition, cleetus!

[Keyser Soze]

We never hooked up, although we dated for a while after my ex and I broke up.

I would call it cheating since,

a) you felt like you had to hide it.
b) you dated the guy afterwards.

Once you hide it, thats pretty much cheating, the fact that you dated afterwards makes it even less innocent. Look at it this way, if the shoe was on the other foot would you have considered what your ex did as cheating if he did the same thing you did and then dated the girl afterwards?