Yes, this does happen I'm afraid. I can totally relate to your problem. Been there, done that, as they say. You try to help someone and then you just end up as bad or worse than they are. That's what happened with me and my ex-wife. Sometimes, it is not that obvious that they have a "broken wing" until much later. That happened to me. It took me several years to recover from that mess, but I have learned to be VERY careful of who I become involved with. Proceed with caution, is the learning I got from it.
But, be assured that not all "broken wings" are lost causes. I have known several women who came from horrible marriages and childhoods, abuse, etc., who owe their present lives to men who cared about them and helped them overcome their issues. I think that the key here is that they need to acknowledge their issues, as does their partner, and they both need to work on them. I would suggest that professional help is really a necessity as well, not to mention lots of time, patience and understanding. If someone does not acknowledge their problems openly, then they are more than likely to just get worse over time.
My other thought is that since some of us have problems ourselves, that we unconsciously seek out those who also have problems. Kind of, the misery loves company, syndrome. I would be cautious of this happening to you as well.
Hope this helps.
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"A man needs a little madness...or else...he never dares cut the rope and be free."
Nikos Kazantzakis, ZORBA THE GREEK
Some of us just have a little more madness than others!