Dear friend,
I have come to believe that God listens attentively to, and answers, our prayers that line up with His will. Since He has made His position on divorce very clear (See Mark 10:11 and Luke 16:18), I believe that you should pray very hard for your husband to come to his senses before it is too late. As Shekaniah pointed out so beautifully with her poem, we (men) often fall prey to wanderlust for all the wrong reasons and then regret it for the rest of our lives.
If your husband is a believer, and you were married in church, you could ask him in a non-confrontational way how his current actions line up with the vows you both took on your wedding day. I believe that you should make your position on the matter clear, but it should not be out of fear. It should grow out of a Godly conviction that marriage is a sacred covenant that should not be broken for trivial reasons. (And believe me, most of the reasons that men will come up with are trivial.)
And always take courage from this fact. There is Someone who loves you far more than your husband ever did, or ever will. Jesus will always be there; to comfort you, to prop you up, and to bear your burdens for you. In these times of trouble, you should rely on Him to guide you through.
But, again, let me encourage you not to give up without a "fight" (although fighting is the last thing you want to do right now). Remember, in a broad sense, God is on your side. Tell your husband how you feel and ask him to explain his reasons for wanting to divorce you. Then be prepared to address his concerns, truthfully and lovingly. It may not work but it is worth a try.
God be with you in your struggle.