Lily broke up with James when she realised that she had a crush on Severus but it was too late. Severus had a crush on James and Sirius and he is gay. James realised after Lily broke up with him that he liked Sirius and Severus and he was Bi. Same with Sirius he had a crush on Remus but Remus had a crush on Regulus so he fell in love with Severus and James and he is gay.