Here's what I have been able to find out after being very discrete (this is not something you just start chatting casually about):
She started dating this guy who was a cop and they went out for about a year. She eventually felt things weren't what she was looking for and, about a year and a half ago, broke up with him as gently as she could. She's a very nice person and wants to be good to everyone, so when she said, "I hope we can still be friends," that wasn't code for, "Please don't hate me," but she genuinely meant it.
They would get together every month or two to do something together like see a movie or some other friend/social activity. She had no idea what was going on in that heart of his.
About two months ago, he suddenly declares he would like them to get back together. She says no, she doesn't feel that way for him. He starts calling multiple times a day, sometimes multiple times an hour, showing up unexpected at her house, and so on.
Then, this weekend. She was at a graduation party for a friend of hers. He wasn't invited. He went there anyway (he knew where it was and when it was because of her and her friends' Facebook pages. In case you wonder why I try to keep specific details of myself offline and everyone else should, too). He goes around to the backyard, sees her, draws his police issue revolver and fires five rounds into her.
The last round? It's for himself. The old murder/suicide thing (which I've never understood. You think you're going to be together in the Afterlife, but you just committed murder. You ain't riding the same train as your victim). He puts the gun TO HIS NECK and fires. Knocks himself out, but doesn't kill himself.
He's in the hospital right now, restrained to the bed as he is considered a "flight risk". Ya think? Video court session, he's to be tried for homicide, arraignment is scheduled in a couple of months. The only bright side to this is he's a lower-order critter in the police chain. No connections, no power. Cops like that don't do very well in prison with a bunch of criminals who don't like cops.
I mentioned this is a warning. I'm not kidding. As demonstrated above, there might be little signs here and there, but when the switch gets flipped, when it becomes critical, that obsession takes over, you have to act fast, decisively, and without mercy or they will turn your life into a living Hell. Or maybe end your life.
When a guy acts like a creep, don't write it off as a deep personality. He's dangerous. Run from him. Too many people are exactly as they present themselves, and the only reason they don't harm you is they see no reason to. And if they suddenly think you are denying them what they should rightfully have (i.e. you), they will act.
It's like kicking over an anthill -- do it fast, do it right, or the buggers will eat you alive. If you aren't comfortable with guns, find other ways to protect and defend yourself. Keep an eye out for behavior that crosses lines, and take action right away, whether restraining orders or just letting him know you won't be fucked with. DO NOT GIVE HIM UNDERSTANDING OR ANOTHER CHANCE. Bad behavior rewarded is bad behavior repeated. It will only embolden him or make him adjust his plan so that, it may be a different path, but he still reaches his goal.
I know men can be stalked, too. It happened to me. But statistically, women are at far greater risk not only of being the focus of this, but often the behavior women are subjected to is much more severe. Take some basic self-defense. Be aware of your surroundings. If a guy's behavior seems the slightest bit off, there's a reason for that and you should run away.
Please take these words to heart.