"True love"

Either in the "you have one person you are destined to be with" form (you don't, there are tons of people you could end up having a wonderful lifelong partnership with)

Or in the form of "romantical love will bowl you over with the force of its passion" (I think David Foster Wallace had an essay about this in Brief Interviews with Hideous Men, but the idea is that many people just want love to come in and make the decision for them in their romantic relationships, but the reality is, it's a choice. You have to choose to be in love with someone, and choosing it over and over is what makes it beautiful).