Angele,

I assume that the wife is you in this?

You are asking why he would do this to you.  You and everyone else here can give a dozen different reasons but ultimately it does not matter.  What matters is knowing that your marriage is over.  The sooner you come to grips around this, the better off you will be.

Kick him out of the house, change the locks, get legal help and therapy for yourself to deal with this betrayal and dissolution of the marriage.  Only communicate with him through your lawyer.

Mark