Commitment and Chores

I wonder sometimes, what it would have taken, to be accepted by my ex, as the only love of his life. At one time, I used to be, but I don't know what changed. What makes someone commit to loving one person, then , somewhere along the way, they change their mind, decide it's okay to take that leap of going out and having an affair behind their spouse's back? Why would he have decided that it was okay? Sometimes, it seems that life is blinding....only because you think that everything is okay, but they really aren't.
Making a commitment of marriage or being in a committed relationship should be just that--a commitment. Do we just suddenly grow tired of the same ole every day life experiences? Is there any way to change this?
I just feel that life is life....bills still have to be paid, no matter if it's a truck note, house payment or just the monthly electricity or water bill that comes along....and kids, if you have them, need to be nurtured and cared for.. Cooking dinner, washing the laundry all has to be tended to, unless you have a daily maid to do it for you, so once the newness of a relationship or marriage wears off, and daily life is staring right directly at you, these are all things that must be taken care of. Do we get so caught up in life that we let go of our newness of vowes? Aren't they just as important as the chores, if not more so?