What if, one day, your best friend decided that they didn't want to be friends anymore? Not because of something that happened like a fight or some offense. You didn't say something stupid while drunk. It's not anything that can be apologized for or mended. It's much worse than that. It's just you.

Ask anyone it's happened to: Short of the death of a loved one, there are few things as devastating. Not even the end of a romantic relationship can quite compare. Those, we mostly understand, can come and go. But a friend who doesn't want to be around you anymore? It may sound like playground troubles, but whether it happens when you're 8 or 80, that's a wound that never really heals.

Yet it's also not a topic that's been widely explored in great plays, films and literature. Maybe that's part of the reason it's such a blow when it actually happens: The art wasn't there to warn us.

And who better to stare into this uncomfortable well than the great playwright Martin McDonagh? In " The Banshees of Inisherin " he and a small group of wonderful actors have sculpted an aching reverie about friendship and fulfillment that is one of the very best films of the year.

It's 1923 on a small island off the west coast of Ireland when we meet Colin Farrell's Pádraic, a happy and kindhearted fellow who is content with his life there living with his sister, the bookish Siobhan (a brilliantly sharp Kerry Condon), tending to his favorite donkey, Jenny, and meeting his best friend Colm (a quiet, soulful Brendan Gleeson) at the pub every day at 2 p.m. But on this day Pádraic's routine is upended when he knocks at Colm's window to go get their daily pint and Colm ignores him. As Pádraic will come to find, Colm has decided he just doesn't like him anymore and would like to spend the rest of his days doing anything but talking to him. For Pádraic, this is just the start of an agonizing spiral of self-doubt that turns into a nightmare and leaves no one unchanged.

Colm's decision, everyone agrees, is mean. Really, really mean. It's something you just don't do to a person, especially someone like Pádraic who values niceness above all else. But Colm has and isn't budging.

People also seem to agree that Pádraic and Colm always made an odd pairing. Pádraic is affable and kind and maybe a little dull. Colm is a more tortured soul, a musician and artist and reader who feels his own enlightenment is being stifled by boring chats. Mean, but also true, at least to Colm who in millennial speak has chosen boundaries and self-care at the expense of another's feelings.

"The Banshees of Inisherin" presents an impossible conundrum and there's no solution that will make everyone (or anyone) happy. It is a McDonagh joint after all, and Carter Burwell's melancholy score and Ben Davis's haunting cinematography add to the spiritual solemnness.

Farrell is as heartbreaking as he's ever been as Pádraic, who we watch in horror as he slips into a crueler version of himself. A sweet and tragic local boy, Dominic (a perfect Barry Keoghan role), steps in and for a minute looks like a glimmer of hope for Pádraic. He's also possibly repeating the cycle of how Pádraic and Colm became friends in the first place — some combination of proximity and lack of options on a small island.

This is the nature of life on an insular island and it's a problem for more than Colm. It's starting to gnaw at Siobhan as well.

The film may leave you shattered, but it'll also have you laughing, quoting lines in a bad a Irish accent and thinking about your own life and relationships. At the start, it seems clear that Colm is the unreasonable one, but as the story progresses, you begin to accept and maybe even admire his resolve. Somewhere along the way you may find yourself just praying for Pádraic to accept it too and let Colm live in quiet peace.

"The Banshees of Inisherin" is a rich, soulful journey, full of agony, dry Irish wit and big, haunting questions. If it's answers you're looking for, however, you're not going to find them on Inisherin.

"The Banshees of Inisherin," a Searchlight Pictures release in theaters Friday, is rated R by the Motion Picture Association for "language throughout, some violent content and brief graphic nudity." Running time: 109 minutes. Four stars out of four.

Lindsey Bahr is an AP film writer