People feel guilty when they cheat. So they try to distance themselves from you so they don't show their guilt, or maybe accidentially say something they didn't mean to. Also, a couple that drifts apart might result in one of the partners looking for affection elsewhere.
Make sure you talk regularly, share your thoughts and dreams and concerns. Speak up if there's an issue in a constructive manner, to find a solution. Don't let things fester or your worlds drift apart.
This tip was submitted by an anonymous visitor to our website.