The Story of Us (1999)

Extremely well written and ultimately touching comedy drama about a couple and their marriage. 

Ben and Katie (Bruce Willis and Michelle Pfeiffer) choose to separate when the children are away on summer camp. We see them working through the new relationship status, while looking back on the highs and lows of the marriage. 

Director Rob Reiner (who also stars as a family friend) wisely keeps the film simple and focused.