What if at some time in the past, you've said "no" to the person who could have been right for you? What if you dated and then left the one who could have turned out to be meant for you? What if you never gave The One his chance (or time enough) to become The One? Then you're pretty much screwed, right?
But on the flip-side...
What if you say "yes" to his advances, end up dating, stick and not leave, give him a chance to be The One, get engaged, get married... and then wake up one morning realising that you married the wrong man? Then you're screwed, too, no?
Ugh. Relationships are a landmine of what-ifs!