Of course it's true. Here are some more additions from the comment section of that reddit submission.
When we were younger and free I've forgotten how it felt before the world fell at our feet --- Referencing their prior relationship and the possibilities before they both became super-financially successful in their fields.
To tell you I'm sorry, for everything that I've done, but when I call you never seem to be home --- He had trouble getting in touch with her after they broke up and then again after he tossed her number. Also, he goes to their house when he is back in the real world, and she is not home/does not live there.
It's so typical of me to talk about myself, I'm sorry --- It's clear throughout the movie that the person Jack became was extraordinarily self-involved. He begs to buy a suit that is $2400 when they are poor. He talks about moving to the city to pursue his new career and disregards the family's needs, etc.
I hope that you're well. Did you ever make it out of that town where nothing ever happened? --- (Another interpretation) The "town" being metaphorical, referring to waiting for him to come back from London and continue their relationship, which never happened. Basically asking if she was able to move on.
Another wrinkle: Adele the secretary is the one that tries to get Kate on the phone. I imagine Jack left and Adele called...