In most cases no. But if it was in the beginning of the relationship when things weren't serious, possibly. Not that I'm encouraging cheating, but people do make mistakes.. It doesn't mean that it's going to happen again. I don't believe in the saying "once a cheater always a cheater" A mistake you make can't define who you are as a person.. If I try smoking once in highschool, does that mistake make me a smoker for the rest of my life? No. Some cheaters will change, some won't, just like any other mistake.
But if someone had the nerve to cheat while we're in a serious relationship, it would make me question how serious they were about me. I don't just give my trust to anyone, so it would be nearly impossible for a guy to get my trust back after cheating,