My fiancee cheated in his last marriage and it worries me.

The main thing is, do you trust him? I don't condone cheating at all, but I do believe there are people who have cheated, are genuinely sorry and work to regain the trust of their partner and never do it again. I don't think any bad behavior is destined to be repeated. However, the thing that would concern me is the lack of regret or shame. To me, the people who would cheat again are the ones who never thought they did anything wrong in the first place.

So perhaps you know something you don't want to face and admit to yourself. The old saying "once a cheater, always a cheater" has some fact in it, that's why it has persisted. However, if you've got doubts, think it over before you marry him...