The brooding, depressing feeling that overtakes you upon realizing that the object of your desire doesn't return your affection.
"When Captain Whiskers ran away from home I was so heartbroken....."
"I thought everything was going great, and then she suggested that I meet her boyfriend because she thought we would get along really well. I was pretty heartbroken."
"I became very heartbroken when the girl I had a crush on told me every painful, depraved, and humiliating detail of her sexual history."