4. Once
One of the more acclaimed films from Ireland, Once tells the tale of two musicians referred to only as "Guy" and "Girl", who within the course of one week meet, write songs together, begin falling in love, and record an album. Along the way he learns she has a daughter, lives with her mother, and has a husband in the Czech Republic that she no longer loves. She learns he had his heart broken recently when his long time girlfriend cheated on him and moved away. Throughout all this, they continually grow more attached to one another, even to the point of the Guy inviting the Girl to move with him to London, child and all (though isn't so eager about her mother coming along).
The Bittersweet Ending: After they finish recording their album, the Girl reveals to the Guy that her husband wants to patch things up with her, and is moving to Dublin to be with her and their child. The following day, the Guy leaves for London, but the Girl can't bring herself to see him off on his flight, thus never being able to say goodbye to him. At the very end, we see the Guy calling his ex-girlfriend in London, whom he learns will be very happy to see him again. However, just before his flight, the Guy buys the Girl a piano and arranges to have it delivered to her.