Haven't watched pass the 1st episode but in Temptation with Kwon Sang Woo and Choi Ji Woo he is married and I think in the end the wife cheats too.. Just remember understanding it ain't my coup of tea. (a dissapointment for those who waited for their reunion in a drama)
I Have A Lover - it's 50 eps but I think it's interesting enough. The guy cheats on her and actually gets with the other girl (who btw turns out to be a total bitch, just wait for it), some amnesia and such and more cheesy a little overused themes but I keep waiting for him to suffer for what he did. (haven't finished it yet)