The only time in my life I ever remember crying over a(n international) cricket match was the Fourth Test of the 1999 series against New Zealand. There was seemingly so much at stake, and England lost. That said plenty about me as well as the game (I was 13 at the time and had just begun to get properly, fully into international cricket) but I guess that's the point of this thread. I doubt, had I been born 8 years later, that I'd have felt any different at the 2007 loss to India, which was probably the 2nd-worst I've ever felt. That is, the time when I realised England had no chance of winning the Third Test and squaring the series, which was probably not long after the toss on the opening day.
There's something about Test series defeats at home to teams other than South Africa that's really horrible. Fortunately I only have strong memories of 5 such things - Pakistan 1996, Australia 1997, said aforementioned, and Australia 2001.
Partly because away defeats take place during non-regular cricket hours, and partly because I value home superiority so much, I don't and never have felt anywhere near so bad about away defeats, though like most the final day at Adelaide in 2006/07 rates about as low as it gets there.
But the best I felt was unquestionably the last day at The Oval in 2000. England had won the Wisden Trophy for the first time in 31 years - I was 14, the previous occasion was 16 years before I was born. How much better can it get? Fair to say, of course, that as that Pietersen (and Giles) innings on the last day in 2005 progressed, things got closer and closer to that 2000 feeling being equalled.