To answer OP, yeah I've cheated.
The other girl found my gf on FB and dropped the bomb when she realized her usefulness extended only as long as I was granted access between her legs.
I felt terrible when my gf told me she knew. In the parking lot at the mall.
Put me on blast in front of my brother in the car.
The betrayal in her eye.
She took me back but we didn't stay together in part because a few months later I headed to college and she was still in high school due to her being a grade behind me.
She's my friends sister and so we still speak. The sexual tension and chemistry is still there but I doubt we'd ever get back together and date seriously.
At most, we'd get physical but that's about it.
Once that trust is broken, it's hard.
I'm in a LTR now and haven't cheated but I've come close and I do enjoy flirting.