Sometimes, a lot of heartbreak is self-inflicted in the sense that what causes it is what you imagine rather than actually what happens.
For example, my crush is honestly just an acquaintance. I brought up the concept of falling in love with a phantom because when it comes to the details I don't know (or even those that I know), I invent them and become attracted to that part. That's how some people "fall out of love," when they actually meet their crush and find them to be the opposite of what they imagined (or fall short of their standards). And honestly, no one's telling you to fill in these gaps. But I think it's normal human curiosity to fantasize and create these "phantoms" in much the same way the Greeks created their pantheon.
And then there's the fear that arises from lack of communication. Again, these are all imagined. It might be the boyfriend who starts worrying because his girlfriend isn't responding to his calls or text messages (never happened to me because I never had a girlfriend in the first place). Or a wife worried because her husband is late (i.e. is he having an affair?). And this isn't limited to lovers. It could be anyone in a relationship, such as parents and their children (i.e. why didn't you immediately come home from school? You could have been kidnapped!). These worries tend to be flights of fancy, unlikely possibilities, and it's our creativity that gives rise to them.
Oh, and the one time our fears are actually true, we expect that all the rest to become true as well.
You do know that the stereotype of the writer is that they have fertile imaginations right? I wonder what they're thinking of their absent significant other right now.