Karin, i agree with you.
I was in a LDR, and before I went away I told my then bf that if he did cheat, I would want him to tell me, as lying would be more of a problem than infidelity. He did cheat, and told me me six months after...which means that there were several times where I had asked him and he lied to my face, and it was the lying that killed the relationship. He cheated again and told me straight away, and it wasn't really an issue (both were one night stands), but I never really trusted him again because of the lies the first time.
I don't think things are ever black and white. I was thousands of miles away, he wasn't going to see me for six months, he was a good looking chap who couldn't take his beer...I sort of expected it to happen, simply because he was/is a weak man!
A long term affair I would not have put up with. I value honesty too much.
Vicky