There are several intertwining stories here, so bear with me on this:
Bradley's (Greg Kinnear) wife Kathryn (Selma Blair) leaves him for Jenny.
Bradley starts dating and eventually marries Diana (Radha Mitchell), who has been having an affair the entire time with the married David.
David's wife finds out about the affair after Diana and David have broken it off, and they separate. Shortly thereafter Diana leaves Bradley and gets back together with David.
Bradley slices his hand open and goes to the emergency room, where he meets Margaret, his doctor. They start dating and it seems he has finally fallen in love with someone who loves him back.
Bradley runs a coffee shop wherein works Oscar, who falls head over heels for Chloe.
Bradley's best friend and a frequenter of his coffee shop is Harry (Morgan Freeman) who, together with his wife Esther, are mourning the recent death of their son from a drug overdose.
Oscar and Chloe move in together. Chloe visits a pyshic who tells her Oscar won't live long. So, she asks Oscar to marry her and throws away her birth control.
At their wedding Chloe tells Harry that she's pregnant, and asks him if he and Esther would be willing to adopt them, as they have no parents. He thinks she's just being kind, and does not respond.
Oscar dies of a congenital heart condition when she is heavily pregnant.
Harry asks Chloe to come live with he and Ester, promising to love her and her baby with all of their hearts.
Thanks Mary C!