Pray. Pray like you have never prayed before. Pray for wisdom, pray for guidance, pray for help. Most of my prayers in the beginning didn't even contain words, just formless cries to God.
Be in the Word. Some days all I can do is read some Psalms and Proverbs. But being in God's Word is how he communicates with us, and right now you need to hear from God.
Gather Godly people around you. Find people that you can trust with this information. God's people are called to help each other in times of trial. Do not stay isolated and alone.
If you aren't already in counseling I would highly suggest you get into some sort of Christian counseling. I know my therapist has really helped me.
Those are the main points that I can think of right now. I know a lot of people would say, you know what he cheated on you, you are perfectly justified in asking for a divorce. Even the Bible says divorce is ok in instances of infidelity. But that doesn't mean that I have to ask for a divorce. Marriage is ordained by God, and I see it as my responsibility to God, to myself, to my daughter, and even to my husband to do everything that I can to work things out.
I won't pretend this is easy. Alan still hasn't given her up. Thank God she does not live here. I am having a hard enough time know that they are communicating every day. I'm not sure what I would do if I knew they were seeing each other in person.
Right now I am just trying to take one day at a time, giving God time to work. And I do believe that He is working.