Adultery is harmful to self and other. Buddhists consider it sexual misconduct.
If I HAD to choose between cheating on my loved one, or him cheating on me, I would take the latter. I could not forgive myself. I wouldn't. It would haunt me and I am not into rationalizing my choices or living with regrets.
I've been married for over 25 years and I've been faithful the whole time. I've been tempted a few times.
Just think, there was a time when that was nothing to be proud of. Times have really changed and I am happy for you that you haven't disappointed yourself. I was reading a love letter from a husband from a few years ago and it surprised me when he said, he had never thought of being with another woman other than me, and how it hurt him when I had told him I had thought of being with another man once, but that's as far as it went.
So much for honesty.... The positive side of that is I learned one doesn't always have to confess everything, if it serves no positive purpose. [We had been in marriage counseling]