Do you trust your partner?

I've had this discussion with my wife on many occasions now, as one of the most argumentative subjects in relationships comes into question.

Okay, here's the deal:

One man, who shall remain nameless, is in a relationship for around five years, but it's a relationship that hasn't really gone anywhere, and just seems to be plodding along as matter of convenience rather than a full out and out love story.

The man makes all the effort to travel over to his girlfriends' house all the time, and very rarely sees the opposite happen the other way round where the girlfriend makes her way to his.

Then five years into the relationship, the man ends up seeing a beautiful woman on a picture of a friend that he works with, and a week later is introduced to that beautiful woman at a works team night out.

He then decides that he likes the look of this beautiful woman and gets talking to her, and wants to see her again, this during a time when he was still with the other woman.

Then three weeks into the newly found relationship, he gets an ultimatum to either finish with the one he's been out with 5 years, or to end the possible relationship with the beautiful woman.

So, he decides that he wants to end the 5 year relationship, and head for new waters, and that's exactly what he did.

Ten years on that decision proved to be the best, as engagement, followed by marriage was the outcome, and right now it's a happily relationship.

Trust though, seems to be a different issue, as the "cheater" tag is always at the back of the good lady's mind, and the fact that as a saying goes, 'a leopard never changes his spots' - which I always battle against as this is a whole different relationship to the one I ended, as that felt just like it had run it's course.

What would you do?

Would you trust someone 100% who had "two-timed" previously, or would you give them a clean slate?

By the way, I trust my wife 100%.