It's Complicated (2009)

Jane (Meryl Streep), a successful restaurateur, has been divorced from Jake (Alec Baldwin) for many years, although they remain friends. When an innocent meal together turns into an affair, Jane finds that she is the other woman in the now-remarried Jake's life. Meanwhile, Adam (Steve Martin), an architect hired to remodel her kitchen, is still stinging from his own divorce. He finds himself falling in love with Jane but soon realizes that he has become part of a triangle.