My guppies do this, they swim in circles around each other not losing sight, i'm sure they are male as they both have bright orange and black tails and the other is blue, i have 3 males and no females because the lady at the lfs said that they had been raised together without females and adding them now would cause them to fight between themselves for the female attentions. So to leave it as it is
I assume they are just playing as they swim happily most of the time together