SummerMan, I've been thru multiple long term jobs and all I can say is that the grass always might seem greener someplace else, but more often than not there will be something else you will not like about the new job (weather, co-workers, environment, etc.)
It sucks working in the winter, I know how it is, but life has a way of balancing things out. Yes, the weather is nicer down south, but job prospects in the south really suck, and do you really want to lose the seniority that you've worked so hard to get?
Listen young buck, you've got co-workers that are cool, a route you can call your own, your making decent money now with top shelf benefits for your age and in 2 years you'll be making more than a lot of people who are much older than you who have to play office politics. (I hope your maxing out your 401k). On top of that you've got strong UNION backing.
I think the combination of the winter blues + the fact that you lost your girlfriend just magnifies the whole situation and you just want to get away and forget how crappy it feels. If I hit the nail on the head, then DON'T ever back down and run away just because you feel crappy or don't ever run away just because of ONE girl. There are a billion girls on this planet to choose from and if she is not down to ride with you, that is her loss.
Remember, what doesn't break you can only make you stronger. Now go in to work, brofist your teamster bros, and run your route following the methods. After work pop open a few cold ones with co-workers cause this buds for you. By next summertime you'll have yourself another hottie willing to ride the brown monster!
"You can't choose what life throws your way, but you can always choose your attitude!"