Are you a cheater if...?

Teri

So I’ve always wondered this:

If I slept with a man and I didn’t know he had a girlfriend because he kept it from me, have I cheated? I feel like no because I didn’t know I was doing anything wrong.

Secondly:

If I was single and I knew this guy had a girlfriend and I kissed him/performed oral sex in him, have I cheated? (This girlfriend he professed to not caring for anymore), and who he broke up with a month later.