Actually the most common thing that American couples and one of the biggest contributors to martial fights and such is money.
With me and hubbie, its a trust thing. I trust him enough to want to spend my life with him and have his children. I also trust that he will be faithful to me as I am to him.
If you don't feel fullfilled in some way or another, you should communicate that to your spouse. If you need to be stimlated spiritually, recommend you find a faith that you both can share. If you need something sexually, suggest something to spice things up. I think that is the biggest problem with marriage. People just stop talking to each other.