What's the half-life of a crush?

For the non-science types, half-life is the time it takes for something to decrease by half.

I’ve heard a lot of people say the “honeymoon phase” of relationships only lasts about 18 months, and after that, the relationship is based on commitment, companionship, shared interests and values, etc. So surely a crush, which has none of those things, should start decaying well before that point. Right?

So how long should it take until a crush has decayed to one-half of its initial crush level? What’s the longest crush you’ve ever had?

Or do crushes not fit an exponential decay model? Do they expire suddenly all at once?

Bonus question: Do you think it’s fun to have a crush, or is it just agony? (I am working off the assumption that a crush, by definition, is at least mostly non-mutual. Right?)