For me, it was Tool. Even typing the word makes me want to vomit in my mouth. Sophmore year in high school, getting stoned in the parking lot, listening to Tool and A Perfect Circle. I swooned, I owned a velvet cape, I had lots of different lipstick tubes and pipes. I finally realized the romance was over when A Perfect Circle released eMotive. I was horrified. Don't even get me started on Puscifer. I was suddenly exhausted by everything Maynard James Keenan, even though I still love his voice. The romance was over.
Tell me, who did you break up with? What happened? Share your heart ache.
Thankfully I got into Tool a little later and can still enjoy them. A Perfect Circle is decent but pretty mediocre rock, but I still enjoy listening to them - as you said, gotta love Maynard's pipes, the man can really scream... As well as convey emotions (mostly anger, disgust, but a range of others too) as though the things he's singing about are actually there before his eyes during recording. Puscifer is mostly awful, but there's a few gems to be found there IMO.
For me, it was metal as a genre in general. I abandoned a lot of cheesy power metal bands soon after I started getting into thrash/death/black metal, but perhaps the flagship would be Iron Maiden. They're the band that got me into metal (and playing bass) in the first place, when I'd bought all their studio albums that was about 30% of my entire record collection at that time, and my first big rock concert was Maiden in Helsinki in 2005 (Eddie Rips Up the World Tour, material exclusively from the first four albums - awesome).
I don't know if anything that serious happened that made me upset with the band as such; sure, they put out a bunch of crap albums in the 2000s (with what should, on paper, be their best line-up - the frontman from most of their albums, and all 3 guitarists), and released unnecessary amounts of collections, DVDs and whatnot that reek of record label cash grabs, but I've grown to accept that if a rock band has been going for 20 years, they either retire, spend their time nostalgia touring, or attempt to release new material which is awful in 80% of the cases and makes you miss the old material in 100%. Hell, Snoop Dogg has been collaborating with the terrorists responsible for the state of rap music today for years, and I haven't broken up with Snoop - I just don't listen to his new material.
With Maiden, I just... Got bored of it. Noticed I only ever listened to them for nostalgic reasons, and that was the only kick I got out of the music. Much of the same applies for most metal bands, though; the only ones I listen to with any kind of regularity are Tool, Exodus, Electric Wizard, Reverend Bizarre, Pantera, and Vio-Lence... Got bored of a lot of the cheesier aspects of metal, but also the aggressive side. After the honeymoon phase I began to listen mostly to thrash/death/black metal with relentless drumming onslaughts and "Cookie Monster vocals" as some people refer to them, but at some point I started getting sick of it - and when I did come back to listen to metal, it was rarely the extreme kind (if so, it was thrash - hardly ever death or black). As a teenager aggressive music was a way for me to let off steam without physically doing anything more violent than air guitaring. I guess that as I grew older I had no need for such an outlet anymore... and more need for music to make me go "Ooh" on drugs.
I used to be a walking metal encyclopedia but now I notice that bands I used to listen to have put out 4 albums I've never heard of and changed half their lineup. I still enjoy the music if I'm in the right mood, but I completely abandoned the metalhead that I was.
and funnily enough, this didn't cross my mind earlier, but Bruce Dickinson - I still listen to the Iron Maiden front man's solo albums quite frequently, but Maiden I don't think I've listened to in at least 2 years. Might do so now, in fact.