My prayers are with you. I am in a similar situation, except my wife is the one leaving, I know there is another man, and our marriage was never convalidated nor our two wonderful boys baptised. Still, I would do anything to save my marriage. I, too, know the feeling of wanting to crawl into a corner and die. Just please be strong and have faith. God can save your marriage, but it is up to Steve to allow a conversion of his heart. If you keep the faith, though, God will help you and will work the best good out of this terrible situation. Pray for your husband. Pray for your marriage. Pray for yourself, not just for the grace to deal with the situation, but that God works on your own heart so that you can become the woman Steve needs but that Steve will come to need the woman you are so long as you are the woman God wants you to be.
I know this sounds trite, but give it up to the Lord, and the Lord will smile upon you.
I now that none of this makes the situation any easier or less painful. I am sorry. I wish I could take your pain away, becasue I know it all too well and would never wish it upon anyone.
I will pray for you, your husband, your marriage, and your children.