Most Helpful Guy
First rule, don't generalise. I know this might seem minor, and I know its g@g because men (and women) think similar to the same gender, but that doesn't mean we are all the same.
From what you've said, it sounds like he might have had something on the side? Frankly I don't know, but it could be a 'life-changing event'. Something has happened which has completely changed his outlook on life, and therefore also your relationship, because a decision like this, is not something that is just made on a whim.