It's complicated Movie (2009)

When attending their son's college graduation, a couple reignite the spark in their relationship. But the complicated fact is they're divorced and he's remarried.

When brought together at a family event, two exes find themselves oddly attracted to each other after ten years of divorce. Although the couple think that this affair will stay in a different state, it brings itself back to their own city and disrupts their personal lives. While the couple still maintain other romances, they cannot help but to continue with their affair.