Trust is huge for me. Marriage is hard enough without one side holding back and making it worse by lying. If I trust my spouse I am able to forgive and move forward. If I don't trust her I feel like she is fighting against me and I am less inclined to help or want to help.
After her affiar I accepted her back and said the one thing I needed was complete honesty. She could not do that and now we are heading towards divorce. I laid it down what I wanted/needed, it was up to her to hold up that end of the bargain.