Well it depends on what you consider cheating. Behind my last gfs back I "cheated" twice but I only consider it as once (I'm a girl btw).
The first time I was on holiday (holiday had been booked before I started seeing her) and I slept with someone whilst I was drunk - never saw the person again and would never want to. I don't consider this cheating (although many, would and do, and I understand why).
The second time, I met my (now) current gf and we flirted and met up in secret for a few months (nothing physical ever happened despite her persistance lol), I then ended it with my now ex (current gf at the time) and then started a physical relationship with my now gf who I've been with for nearly 8 years. I consider this cheating.
I consider an emotional attraction or bond as a worse "cheating" than a drunken one night stand, because the emotions involved are a lot deeper and (usually) premeditated and are more devious, deceitful and calculating than a drunken one night. And if you start something physical with someone who you are emotionally bonded with then that's the worst type of cheating.
I (hope I) would never cheat on my current gf but as has been said, you never know what's round the corner - I certainly don't feel like I would ever cheat on her. At this moment in time, she is everythig I want from a gf so my "cheating" on my ex paid off in this instance but I certainly don't condone it and am ashamed to a certain degree how we got together (I always cringe when ppl ask).