Has anyone ever seen a male guppy try and breed with a killi before mine keeps going after my female killi and I can tell it’s not aggressiveness.
Male guppies will try to mate with anything. It won't produce any offspring.
Technically, guppies are livebearing killifishes...they belong in the same order (the Cyprinodontiformes), and all the African members of the guppy family (the poeciliidae) are egg-laying killifishes commonly referred to as lampeyes. With that being said, guppies use internal fertilization while killifishes practice external fertilization like most other bony fish, so barring artificial insemination a hybrid between a guppy and a killifish would be impossible (and even with artificial insemination, the resulting hybrid eggs would likely perish before hatching, as killifish do not supply any nutrients to their eggs after they are fertilized like guppies do...this is ignoring the genetic distance between guppies and any of the egg laying killifishes).