As noted in previous responses this week, the specter of Calum's death weaves in and out of the story. Here are some key sides of dialogue which reflect that point.
CALUM
Can’t see myself at 40 to be
honest. Surprised I made it to 30.
Later, Calum reveals that he's had struggles with drugs, hinting at a troubled experience as a young adult.
----
While Calum brushes his teeth
SOPHIE (O.S.)
I don’t know. Don’t you ever feel
just, like, I don’t know. Like when
you’ve been on a real high, like
something’s been amazing, and then
you kind of crash. And feel like
you’re kind of...sinking or
something like that. It’s weird. I
don’t know.
Calum listens. He avoids his own gaze now...
Of course, Calum can relate. He is probably bipolar, hence, the Tai-Chi, deep breathing, all of that intention to calm himself, suppress his depression.
----
CALUM
You never know where you’ll end up
though. You can live wherever you
want to live. Be whoever you want
to be.
The camera pans across to Calum’s empty bed.
CALUM (O.S.) (CONT'D)
You have time.
The intimation that he doesn't have much more time.
----
CALUM
I’m so sorry, Soph. Yesterday.
SOPHIE
It’s fine, Dad. No big deal.
CALUM
It is a big deal. I’m sorry. I’m
sorry.
In my view, this is the point where Calum realizes, subconsciously or not, that he is going to end his life. He has tried his hardest to be a good father ... to reclaim that place in Sophie's eyes ... but in the end, he feels like he has failed. It cements his overwhelming sense that his whole life has been a failure.
Clues. A bunch of clues in his dialogue and behavior which point to his inevitable death.
We, the audience, live with the growing sense of the inevitable throughout the movie. It's such a sad, bittersweet, and emotionally gut-wrenching story.