As others have said, it happens. Don't want to let it get you too down.
Since it seems to have really bothered you, after a little time for the initial emotion to subside, it might be worth doing a serious reflection on what you didn't like about the session. Fatest way to get better at anything is to recognize you aren't perfect and learn from your mistakes. These things in the long run can be great opportunities.
One approach is to jot down anything that comes to mind about what might have gone wrong. When doing this, it is good to put yourself in the shoes of the players as well as yourself (for instance, you might have enjoyed an extended solo bit with one of the PCs but the other N-1 players might have been bored out of their minds. this can make them much more prone to bad behavior such as rules arguments).
You might then need to refine what you have on your list. For instance, 2 rules arguments: was there anything that provoked it? Player grumpy about something else? You being too much of a stickler about something not really all that relevant?
Then you can prioritize the list looking for the top 2 or 3 things you really care about. (The rest is probably just the normal friction of a normal pen and paper RPG.)
Depending on what these items are, you might then either consider solutions on your own, solicit advice from folks on EnWorld, or if something seems missing from the analysis, you could get some input from a select player or the whole group. One thing I wouldn't do is go straight to the group with a "let's talk about what went wrong" without some analysis on your own part. I find that nearly all players are useless for that sort of feedback without you asking some very specific questions about specific issues.
I've had plenty of crappy sessions and an occasionally crappy campaign. Some of my finest improvements have come from reflecting on what went well, what didn't and what I could do about it.
You seem a seasoned DM but in addition to just learning the ropes of DM'ing better (always possible no matter how many years you've gamed), you also need to consider that the years bring many other changes:
* Your own preferences in fiction or gaming may change.
* Your group composition may change. (In college, I had many players who would spend hours on out of game stuff. That, unfortunately was long ago. I can either adapt my game or struggle with incomplete campaigns.)
* Your gaming frequency may change. More open ended, "players' write the game" styles work okay with the right group and frequent gaming. I find they are terrible with either gamers looking for more direction or less frequent gaming. Might be time to more consciously work a plot.
* Then there are the realization changes. In my youth I was a stickler for 'reality' (such as you can have in a fantasy setting

). Could have summarized my style as "fantasy simulation" first, "game" second. Now it is the other way around.
* A correlary to the previous: my gaming groups' satisfaction went up considerably when I realized that it was not in my interests to let the game take a "we are all in this together approach" and instead realize that I was providing entertainment. It was my job to deliver. Moreover, I am in competition with many other forms of entertainment (movies, CRPGs, online gaming, the list is endless). If I didn't strive to deliver each session, I was liable to have players drift away (scheduling problems are often a sign of diminishing interest.)
Anyway, take this as an opportunity. You might find a few tweaks to your game. Or you might even decide upon a more radical change. Regardless, self-critique is the path to more enjoyment.