Alice loves Bob. Bob loves Alice. However, Alice is crazy. Luckily for her, so is Bob.
Basically, many works of fiction depict two crazy/eccentric/weird people as being "two peas in a pod" and "made for each other". If a crazy character is going to fall in love, you can bet that ther person they fall for and/or falls for them as well will be just as (if not more) insane. Often, shows/movies/etc. will do this to Pair the Spares
or to give the socially awkward and eccentric characters a (usually) happy ending. This can also tend to happen when a resident crazy character's Spear/Distaff counterpart
Compare Mad Love
, in which the psychotic crush is clearly one-sided.