In the early 1900’s Freud and his colleagues were developing new and radical ideas about the psychological makeup of humans. It may not seem so today, but their ideas on love were on target.
They theorized what we believe about love is based on our early experience with our main caretakers. Freud and his colleagues said these early events determine, on an unconscious level, what we experience as love.
Disappointment is a difficult emotion. It can step in and ruin any experience. You are having a good day, something happens where your expectations are not met, and boom! Disappointment sets in, and the experience is ruined.