What we have here is another case of, out of the ocean of words in English, people picking one and trying to make it serve for both itself and its comrades. Being 'clingy,' so far as I know, has never killed anything but a relationship unless it escalates into something else: stalking, forcibly controlling, and various other forms of possessive aggression. At which point the perpetrator is no longer simply 'clingy,' but, as I said, something else. Do stalkers kill? Yes. The same for people who insist on controlling the objects of their desire, obsession, and/or lust (I won't use affection, since no matter what such a perp might say, I don't feel there is any). But in engaging in these behaviors, they've stepped beyond 'clingy.'
On the other hand, I know one woman who complained her husband was becoming 'clingy' because at fifty-seven he stopped being out in a blind with a bangstick in his hand every weekend during deer season. She was ticked because that was when she hosted bunk-o (I have no idea how to spell that) parties for her female friends. They adjusted, though, and that was that. I've also known a woman who was described by her boyfriend as 'clingy' because she wanted them to stay at home instead attending various parties where booze was being served. This was after he'd done one stint in rehab for alcoholism.
Finally, someone who is 'clingy' may not want you to leave, but they cannot 'make' you stay. If they attempt this, they've moved 'up' into controlling, at the least. Hence my bridling at the term used for someone who 'won't let you leave.' It sounds as though some mystic force is being exerted by said clinger. If this was an attempt to indicate physical force, threats, or mental cruelty, then call it stalking, call it controlling or something else specific. But don't simply paint such a wide gamut of destructive behaviors as 'clingy.' If nothing else, to me, it terribly trivializes them, which is the last thing that should be done.