Falling in Love has always been considered beautiful. Whether one is falling in Love with abandon or falling in Love helplessly, the feeling has always been pleasant and warm. Love has been the quest for all humans....and for many other Life Forms.
Yes, Love is the quest for many beings. Whether it is the love for food by the pretas, or the passion for relationship by the Petni, or the lust for human energy by the Penchapechi, the desire for fish of the Mechho Bhoot, or just the Dainee who craves little children, the list is endless.
However, when Love happens between a disembodied being and a human, the confines of body, time and space is broken. The intensity is different, the period is long and the passion is reckless. Why reckless? Because the human is mortal and the disembodied being has time. A lot of it. The pursuit of a companion can then happen over many yugas, many births and many regions.
This should warm hearts and sound poetic. But it is not. It is horrifying.
Why?
Consider this. Memory is an integral part of the process of falling in love. However, a human loses memory when he sheds his body and takes a new one. The disembodied being has no pranamaya kosha. Hence memory stays as long as the manonmaya kosha exists, which could be for centuries.
Now keeping this in mind, let us take a look at a being that falls in love with a woman. It will follow her from body to body notwithstanding the fact that she no longer remembers the being or their relationship.
It gets murkier.
If the human tries to fall in love with another human being, anger ensues. There are several stories of young lovers being separated, the new mate disappearing, strange situations that don't allow the new lovers to meet or get into a physical relationship or even facing untimely death .

There is a solution to break this timeless bond. If an accomplished tantric can erase the memory of the being, the human can finally be set free.
It is not easy.

It gets tougher if the disembodied being was a sadhaka who had put a certain amount of work into his spiritual growth. Then His/Her prowess is stronger and more skilled. Their ability to enter and use other human/animal bodies for their need to communicate with their earthy love, is then put to use. This sudden change in behaviour of people who then obsessively track and follow strangers, confuses and alarms families. You would have noticed people talk about the 'vashikaran' that someone has put on their child and how this has made it extremely difficult for their son/ daughter in their daily routines. The key difference between vashikaran, possession and cross-species love is just intent on a broad level.

On a more subliminal level, karmic consequences are different. Behaviour of the victim is different. Expiry dates of spells are different but the deity is one. The beauteous Kali. Kali puja is adequate to cure all these maladies. Speak to your local Shaman or your family Guru. None of these are permanent.