annoying guppy

1 of my guppies swims around with my 1 male swordtail and tries to nip
at his pectoral fins. at least, i'm guessing this is what he is
doing. at first he used to bother the male swordtail but now he just
sort of ignores the guppy. any idea why this male guppy would be
getting so close to the swordtail's pectoral fins like that? at first
i thought perhaps he wanted a mate and was trying to do something
else, until i got a closer look....

all suggestions welcome!