In men, I believe the feeling of "love" is the tipping point when a shyteload of hormones and unconscious and evolutionarily programmed survival strategies are fired off all at once, continuously, as a result of continued sexual intimacy with someone who happens to satisfy our various unconscious desires and needs.
Don't let my cold biological description fool you. It is the best (or perhaps one of the best) possible feeling to experience.
Nevertheless, it is programmed into us by evolution so that our ancestors didn't get a bunch of cave-women pregnant and then split the scene. Not only for child rearing, pair bonding has a dramatic effect when you consider the increased productivity due to the resultant sexual division of labor.
Since most of it is unconscious, you're not sure when somebody you hook up with is going to give you "that" feeling.
Keep in mind that the creation of "that" feeling happened when people lived in tribes of about 200 or so, so the options were fairly limitied.
Now you pass by 200 different people in the course of an hour or so in your daily life, so the chances of meeting somebody that could potentially give you you "that" feeling is much higher than 10K years ago.
The best way to minimize the randomness (and gain more control) is to do what was suggested over the Oracle at Delphi:
Man: Know Thyself.
If you know your needs, conscious and unconscious, your criteria, it's only a matter of sorting and qualifying.
The process is more complex and cerebral, but the resultant feelings are just as nice.