Leaving a job

Leaving my school wasn't going to be too bad, I thought. Anyway it was miles off. Shortly after that it was the last few days already. Everyone was really kind and I got this sick-feeling in the pit of my stomach of how ungrateful I'd been to all these lovely people. What was I doing leaving this great place?
Then I got stuck on my commute to work again. A mere 2.5 hrs after leaving for work I arrived, having travelled 18 miles. Rubbish. THIS is why I had to change jobs. But how do you explain that to your yr8 students (13 yr olds) who are asking you why you're leaving THEM. Not the school: THEM. I actually felt like a grown-up and like a proper teacher for the first time. Weird how that happens a couple of years into teaching. I had begun to wonder if it would ever happen.
We all know that there are other great kids out there and other nice places to work, but it's a shame this is not normally appreciated until you find yourself in a bad place. Fingers crossed I don't find myself in one of those places next term.