ONE reason?
If it were only that easy.
Let’s just say it boils down to her being a NUT-case!
Hey, don’t tell us, tell Hal! 
As to the OP – he’s arrogant, immature, and not as well-read as he thinks he is (or as I am).
Idiot.
Ex #1 – apparantly, there was “no spark” anymore.
Ex #2 – having asked me to marry him, he went back to Oxford for the weekend, where I found out he was still screwing his ex.
Ex #3 – His roving eyes.
Ex #4 – He was arrogant, childish, and thought he knew absolutely everything.
Hey, whatever history you and Idle Thoughts have, keep it off the boards!
She had dated one of my best friends up until a few weeks before we got involved. While she and I got along fine, I saw how much strain our relationship was putting on my friend, who apparently still had a thing for her. I soon realized I had to choose between them, and I chose my friend.
Now to those getting ready to criticize me for dating my friend’s ex, note that there are some extenuating circumstances:
-
She initiated it.
-
I was a 22-year-old virgin, and hot girls like her weren’t exactly lining up outside my door.
-
My friend gave me his blessing (which earns him, at the very least, the Medal of Honor).
BTW, we’re still good friends.
Ode to a long-departed ex:
She could not cook
She would not clean
She squandered all my gasoline
Although quite bright
She would not work
For monetary gain or perk
A pretty face
And what a bod!
But disposition? Oh. My. God.
Her mama said:
“Be firm and hit 'er”
But instead I up and quit 'er
I got to keep
My clothes and kid
So of her ass, I am well rid
“Hello, Pulitzer Prize Committee? I have a nominee for your poetry award…”
I think music is at least secondary grounds for a break-up. I mean, it probably more than that, but if you’re making a list of pros and cons, music definitely counts.
My ex and I broke up because he hated me, cheated on me, and didn’t support our son (or his other kids). That and the fact that he’s dead.
After the second year in a row of his making his own New Year’s Eve plans, which didn’t include me, and then not understanding how on earth I could possibly be upset about him not including me - when I had specifically said the first year, when he first made plans without me, that I was very very hurt by that, and yet he did it AGAIN the next year - I realized the relationship wasn’t going anywhere, that we had nothing in common, and that he had an entirely different outlook on life than I did.
And then even then I didn’t break up with him until Valentine’s Day rolled around and . . . nothing. No card, no special email, no phone call. I am actually not big on manufactured holidays anyway and would not want to go out on Valentine’s Day - it’s Amateur Night in my book - but everyone knows what day it is and I would expect a boyfriend of nearly 2 years to at least make a funny smooshy lovey-dovey comment about it.
He never once acknowledged my birthday either. And he didn’t see anything strange or unusual about that.
Loser.
Because after 6 years, he still had not married me.
Ex #1 - We were in High School, and he moved away to go to college. Things had begun to sour before that, however. He was occasionally very rude to me, didn’t take my feelings into considerations, and ditched me for his friends. He claimed that I “hated his friends” but in actuality, I liked most of his friends more than I liked him. I just didn’t like the way he acted towards me when others were around. So he got dumped.
Ex #2 - Had a controlling streak that he refused to admit. He absolutely HATED this one particular guy, and I wasn’t even friends with this guy. My best friend’s brother, however, was very good friends with him. So Ex practically forbid me to go to my own best friend’s house just on the off chance that this other guy might be there. Also he told me that if I ever danced with another guy he would dump me. Not that it was a huge deal to me, I just thought it was weird. However, he was wonderful in almost every other aspect, very kind and funny, and we are very good friends now even though it took a while for him to like me again after we broke up.
Sorry. I’ll go back to hiding in secret shame.
Irreconcilable differences…I’m human. He’s Klingon. 
Seriously, he wanted a wife, a family, a girlfriend and couldn’t understand why that was a deal breaker for me.
I dunno. Any history I might have with anyone named Tracy Lord, I’d be happy just for having had one at all. Yowza.
Alcoholism. The final straw was coming home from rehearsal at 10 pm and finding her passed out in the flower bed in my front yard. She’s since begun to deal with it, but too late for us. I think we’ll always be friends, but at arm’s length.
Hey, don’t you mean, “Guy 4: Despite the fact that he is sexy, kind, intelligent, charming, funny, sweet, huggable, fun, caring, generous, dependable, and a paragon of manly perfection who I recommend to all the other ladies of the Straight Dope, we wanted very different kinds of lives.”?
Anyhow, for me (these are all ex-girlfriends, not ex-wives, of which I have none):
#1: We were too young for an LDR
#2: We were better as friends with benefits than as capital-L lovers
#3: I felt more like her big brother/caretaker than her equal partner
#4: She fell out of love with me. Bitch.
#5: I was just a rebound relationship for her, and not really her type. Sadly.
#6: Let’s just say we had very different methods of communication.
#7: Despite the fact that she is a really amazing and sexy and fun individual who I recommend to all the other men of the Straight Dope, we wanted very different kinds of lives.
Religious differences. He thought he was Og and I didn’t.
*One * reason? It’d be a hell of a lot easier to give you ten…
If I have to narrow it down to one general reason, I’d have to say that he’s my ex because although we were supposedly raising a family, he was really only looking out for himself. He would do stuff like buy himself games and CDs on payday, and then if there was money left over and I was nice to him that day, he’d pay a bill. Meanwhile, I was working two jobs and clipping coupons. I’m starting to feel like giving you a lot more reasons, so I’ll just stop right there.
Exgirlfriend: We were youn,; immature, doing it long distance (different colleges). No hard feelings. It was a learning experience.
Psycho Mistake #1: She threatened to stab me. Also she got extradited to Georgia. The two were unrelated.
Psycho Mistake #2: While she was interesting and pretty good in the sack, she turned became a severe disruption in our circle of friends as a compulsive liar and progressively creepy person.
Also, I smoke crack.
Young, dammit.