Miles doesn't kill himself. Well, perhaps at most he does something like that metaphorically -- in that he says goodbye to his old life in the act of drinking that prized bottle alone in the diner.
I wrote this a couple years back on Quora when someone asked "why is Miles celebrating alone in the diner?" Maybe we've all felt something like this at one point.
>> Imagine you’ve been living the last few years with some crazy hope or dream that all the things happening to you are just a fiction and that things are going to turn around. The bottle of wine is a delusional symbol of a life that you’re going to get back — good career, a wife who loves you and wants to have a kid with you. To be opened on the day it all comes true.
Look at Miles’s eyes as his ex-wife tells him she’s expecting a kid with another man. All the hope and fictitious dreaming comes crashing down — that life was a complete delusion, like when you look yourself in a mirror and see, really see, what your life has become and that all the things you’ve been saving that bottle of wine for, just don’t exist.
Not much left to save that bottle for. No one to drink it with and toast over a fancy dinner. Just take it to the grimy local burger joint, drink in sadness to the life events that passed you by, and savor the sublime, once-in-a-lifetime taste of dreams that are dashed on the roadside.