swordtails should be kept in about groups of four... One male to three females...
if one male and one female , the male will mate the female to death.
If two males you take the chance of a territory battle.
IF you do like i did , one male and one female , and the female is a dominant ***** , she will control the male. I dont believe mine was healthy to begin with , and she always pinned him to the bottom of the tank.
With one male and four females , the male should have enough to chase after that he wont pester one female to death.
I have read on the internet that one sword tail will not do well on its own , but after my male died, the female has been by herself.. she seems fine , and hangs around with my zebras. Oddly enough , my Cory cat and frog play together.. chasing eachother to the top of the tank and back down... the sword will sometimes follow along. She never did that when the male was around. She is not a fin-nipper, she just follows with them. Im thinking she is starting to get lonely...
My experience with a single swordtail for ya.