Musicians are inherently unstable. I can say this because I am one. It seems that, many times, the better the musician the more unstable. Many stories are public knowledge, like Hendrix or Cobain, but stories like those are tied into the fame they gained. Some might think that fame was the root cause. While there is a bit of truth to that, fame is not the only cause. I've run across plenty of drama from musicians who were never famous.
One of the first times I played in front of an audience, I met a tall, long haired guy who slightly resembled Kurt Cobain. He played too loud on a crappy guitar, but he had a pretty decent punk rock scream. (Think Tourette's by Nirvana.) A couple of years later I joined a band that he played drums for. Before that time I didn't even know that he did play drums. It turns out that he was phenomenal, an absolute monster behind the set. We played a few shows. I thought we sounded great. We practiced three days a week. Then we didn't hear from this drummer for over a week. After two weeks we found another drummer to fill in for our last show. I never did hear why he quit showing up. I heard he had a heart attack a few years back, less than a year after he cleaned himself up and quit using.
Another time, I was in a cover bar band with an older drummer. He was dating this skinny old hag. She was constantly blitzed out of her mind. One night while we were playing, she was doing her usual routine of humping tables, support beams, chairs, and anything else that was handy. This particular bar had a mentally challenged guy that was somewhat of a regular, and she was so trashed that she didn't notice this guys hand up in her crotch as she was grinding. Or maybe she did, but liked it. I don't know. I didn't ask.
A short time later she was dancing with a fairly nicely dressed guy and kissing him. Our drummer started to argue with the guy over the PA, and when that didn't settle the matter to his liking he started throwing drum sticks at him during Sweet Child O' Mine. I think he hit about four people throwing things in a tiny crowded bar, and soon the two were in each other's faces while we were still playing. (You know it's a very, very long song.*) Our drummer didn't have a great meter even when he tried to concentrate (burn out) much less when he another guy are about to come to blows. I quit playing entirely since I could no longer tell where the beat was, and the rest of the band followed shortly after. Needless to say we fired that drummer. What he does on stage reflects on all of us. I was embarrassed. Besides, I haven't been in a fight since seventh grade, and I don't plan on getting in to one for his dumb ass.
We found a replacement for that drummer so we could get back to slumming it up in the bars. Our new drummer was another one of those monster drummers like the Kurt Cobain look alike, and he had a good meter, whenever he wasn't on something. We played for a couple of years, and then he too disappeared, for about six weeks. When we finally found out that overdosed on heroin, and was forced into rehab.
So why are musicians so unstable? I think it has to do with expressiveness. The best music takes you on a journey, (Pink Floyd and Tool are incredible at that) and real musicians are able to express that. Every instrument is different, has it own personality, wants to be held a certain way. A good musician can feel that and adapt to it. It's not necessarily a bad thing, but it can be a roller coaster at times. I have somewhat of a theory that everyone should date musicians. Musicians are fun, responsive, and intimate. The same instinct that lets a musician feel the personality of an instrument can make a the musician responsive to an intimate person too. (It's hard to explain just try it and find out.)
But if you don't like a musician's flaws... No, if you don't LOVE a musician's flaws then don't marry them or plan on having a long term relationship. (Loving someones flaws is a large subject and I plan to write an entire post on it some time.) If you don't love their flaws then have fun while you can. Enjoy the moment, but know that it's temporary because they will get worse and better on the roller coaster of life and musician's swings high and low tend to be more exaggerated than most.
*The quote comes from Days of Graduation by the Drive by Truckers, and yes I know the quote was actually about Freebird.