I don't know. Neither does anyone else.
You don’t know, but reject explanations of those that study such phenomena.
O…k…a…y………
Similarly, we don't know what consciousness is at all, and assuming that is a phenomena of matter isn't getting us anywhere.
There are questions as to whether or not, or to what degree, other animals experience such. Note that ‘other animals’ is significant because hunans are just another animal. Some animals appear to experience life-long ‘falling in love’. It’s known as monogamy. Others, such as humans, are not biologically monogamous. Humans are considered to exhibit monogamy from a social standpoint.
Also, regarding cheating, just try getting away with that when your whole world consists of 100 people who live right next to each other and do everything together!
Those small groups had that problem. The ancient goat herders knew that such cases existed. Made rules about it that involved throwing stones at the violators until dead. Very enlightened group of humans. And you would assume that this phenoma of cheating didn’t just suddenly ’happen’ at that point in time. This had been going on for a while. The earliest marriages can be dated to about 4000 years ago, (when the goat herders started their book) so humans got along just fine for a LONG time without marriages. It’s thought that ‘arranged marriages’ existed about 10 times longer than the first recorded one. But these weren’t about ’love’, much less the “special sort‘ you believe in.
Your special version of love, fallingnin love, isn’t something new. No reason to think that. And in modern times the resukting marriage fails and ends in divorce roughly 50% of the time. And just that the dact that I know of, or have known of, a lot of people that were miserable in their marriages and yet did not divorce leads me to think that the percent of divorces, which are failures of ’love falling’, should be higher. 7-year itch, cheating, divorces, all indicate that your phenomena, the one you can’t explain where it come from, is just another manifestation of life trying to continue exist.