Why would someone (choose) go to outrageous measures to stalk someone? Why so many lies? So many fake stories?

I am having experiences with this. I am getting scared. I want to put a restraining order and notify the stalker tho she has not done any physical dangers, she simply calls constantly, and researches his present state. She is obessed with my fiancee. Before we got together, they were just talking. After we got together, she became obessive. And she truly belives the stories she tells. She says that they do things together (even with his family), call to say i love you, and he is engaged to both of us, crazy and outrageous things! My fiance and I are really scared, wondering how far she will go; and wonder if she will continue this even when we are married. This has been going on for a year already, and we dont know what to do. Ive researched on stalking, and the types of stalkers there are. I just want to know how a person can lead to this desperate conclusion, and how this can be fixed with the police involved. We've tried everything. And I fear this may lead to a fatal attraction.

Why would someone (choose) go to outrageous measures to stalk someone? Why so many lies? So many fake stories?
First of all, you don't really know the extent of what happened between her and your fiance. I am not saying you shouldnt trust him but just that you never know..You should really talk to him and perhaps ask him if he has lead her on in some way or ..if they had any kind of like, sexual relation or if he promised her something..ya know? Because in that case, her pain and heart break from him could have caused her become depressed and angry and, even you know..a bit crazy..? That doesnt give her the right to "stalk" you..and call you the way she does..you should definately look into taking legal actions at least for the phone calls but of course you cant stop her from thinking about him, or "researching"..for that you can only hope that she will get some help. She could just be hurt. Having the police talk to her or like, scare her or, make it someway that she cant call you will hopefully detour her from wanting to contact. good luck.
Reply:I would go to the police and ask them what to do. One possibility is filing harassment charges. The police (or even you) should be able to get phone records to prove it. It sounds like she may be mentally ill, or she may be doing it for attention. If it's possible to ignore her (i.e. not answer the phone if you have caller id, and not respond to messages, emails, etc) she may lose interest because she's not getting a rise out of you.