Jeff, as I said to someone else before, running is a lot like other things in life. You wouldn't expect to be happy every single day between here and October. You want the majority of days to be happy days (I assume), but once in a while something will go wrong and it'll put you in a bad mood and that's ok and perfectly normal. So that's a lot like running. Not every run will be good (mentally and/or physically) or fast (and this is true for long runs and short runs). But the key is to realize that this is normal and as long as you keep the balance so that you're having more good runs than bad runs then you're doing it right. If that balance tips and you're having more bad runs than good, then it's time to look at factors like training intensity, sleep, diet, etc. but it doesn't sound like that's the case.
As for motivation, I've learned the only way to get myself running is to sign up for a marathon. The other distances I could pretty much go out and wing (not that I'd run them well, but I'd finish them), but I can't do that with a marathon. So every morning I get up knowing in October I'm holding myself accountable and what I do today will determine how much fun I have in October. In terms of burnout, when I'm truly burned out (and not just lazy/busy/etc) I take a day or two off. Better to lose a day or two than overtrain or destroy your knees because of sloppy running form (I learned that lesson last year and have the pictures if you'd like!) And I find by the end of those few days I really want to be back out there again.
I've also realized that running for me is like therapy. When I'm in a bad mood, I go running to get out of my house and my head and try to leave it on the pavement. When I'm in a good mood, the grass never looks as green and the sky never looks as blue as when you're running by it. Then there are weeks like this week where I'm out of town and it would have been easy to have left my running shoes behind. But instead I was able to meet friends, see the sights and really enjoy my time here in part because of my hobby. I'm a lucky girl to be a runner!
I do today what you won't, so tomorrow I do what you can't.