Did you do anything which makes him feel he is betrayed?
I can understand that those men who are not honest with their wives will have a similar feeling.
It could be a woman that played with his mind.
But wait, why people makes love relation outside the marriage domain and then marry after?
From my prespective point of view, love relations before marriage is a wrong step and it is also a weak foundation which can fall down any time, and here I can say what starts wrong most of the time will end in a disaster or unwanted situation.