There's a great
Wiki article on the 7 forms of relationships. I summarized it a couple weeks ago in
another post. It covers platonic and romantic love, as well as companionate, infatuation, empty love, etc. Very good read, simple too, and it has pictures!
Hoe do you preemptively figure that out? You don't get romantically involved with a person until you've known them long enough for the infatuation to have worn off and you've interacted with them in a wide variety of situations over many months.
So, if you meet somebody new and interesting, I figure you can figure out whether you're compatible for the long term by spending time assessing that. If you're more afraid of not being compatible than you're optimistic about it working out, be friends for a couple of years first. Otherwise begin dating to figure it out.
Based on my personal experience, I totally disagree.
3 days into our "7-day-long, sex-free first date", I knew how I felt about my now-husband, and that I never wanted him to be out of my life. That was three and a half years ago, and it just gets better and better every year.
The honeymoon "no problems, no arguments" phase (what you call infatuation) has long since worn off. We have our issues, like any couple, but we have that "special something" that makes us want to work them out rather than hit the road.
I guess I just believe in "true love", because I've found it (cue cheesy music). It's sort of like an orgasm: if you have to ask whether you have it...
you don't. If you meet someone and there's any question whether you could spend the rest of your life with them, you probably can't. Because when you meet that [those] special person [people],
you just know. At least, that's how it was for me. YMMV