Even the best relationships are not immune to this issue.
In a perfect world, with perfect people, this would not be a problem.
BUT, the world is NOT perfect and people are fallible too.
To take a "get over it" perspective with a spouse is naive and disrepectful.
In a relationship - whether married or not - when one suffers, both suffer. When that suffering (or pain, or confusion, or whatever) comes from one inside the relationship, then everyone is hurt.
When one spouse has an issue with third party relationships, it's my belief that it's not out of distrust of their spouse nearly as much as it is distrust of the third party.
No one wakes up one day saying "I'm going to compromise my relationship today". The compromises occur in little baby steps until suddenly "the leap" is not too far at all. I've seen it time and time again in my friends, and it pains me everytime.
I'm glad that there is a happy ending and that you shared your story with us.
If you don't grow where you're planted, you'll never BLOOM - Will Rogers