I never thought this would happen to me, but the last year or so my wife and I seem to be drifting apart, and now for the first time I'm daydreaming about how good it would be to have an affair with another woman. Is God maybe leading me to start over again?
No, God is not leading you to "start over again" by having an affair with another woman - not at all. The Bible is blunt: "Can a man scoop fire into his lap without his clothes being burned? ... A man who commits adultery lacks judgment; whoever does so destroys himself" (Proverbs 6:27, 32).
But God is leading you to start over again in another way - and that is in your marriage. God brought you together as husband and wife, and when you were married you took a solemn vow before Him to be faithful to each other as long as you both would live. God takes that vow very seriously - and so should you. Jesus said concerning marriage, "Therefore what God has joined together, let man not separate" (Matthew 19:6).
How do you start over? Begin first by committing your marriage - and your whole life - to Jesus Christ. God loves both of you and is more concerned about you and your future than you are. He also wants to help you rebuild your marriage by basing it on Him and His will.
Then, take practical steps together to turn back the clock - and even make your marriage more solid than it ever was. Spend time together ... learn to communicate ... pray about your problems ... seek God's will. It may take time - but with God's help you can stop the drift and discover the joy God has for you.