It makes me sad that we can't clear the air with both of them on this last day, but...well, we can't be in two places at once.
I know their friendship probably won't break, but...the idea of Colby going home and crying himself to sleep, thinking he'll always just be the third to their duo, or Austin thinking he's screwed things up again and he's a shit friend–and them just stewing in that feeling for the next few years while they're all away...it hurts to think about. To think how much they'll have distanced from the other two when they meet again.
I chose Colby because he more clearly needed comfort in the moment, but I know they're both hurting; being vulnerable just doesn't come natural to one of them.
Needless to say, for a short story, these characters-- while down-to-earth, or even mundane-- were very compelling! There is a lot to say about them, a lot I can't put into words, and I hope we get to see them again at some point! Maybe in one of your short (text) stories?