What makes you worry about lying and cheating? That comes from somewhere for you to be thinking of it so much. If your relationship has broken down consistently over the last 4 years there is something there which is a causator. If the causator has been trust or lack of it then what is there to the relationship?

Trust is usually only a causative factor if it has been broken one or more times. I urge to you think carefully about the reasons you feel the way you do and be honest with her about your feelings. Honesty is a good place to start a decent relationship.