There is no such thing as third sex. Indeed there is only a man and a woman. There are people who are however labeled as Lesbian or Gays who is said to belong to the ‘third sex’ for the very reason that they are loving someone of the same sex.
Nevertheless, everyone has to understand that loving is an act of our being a human being and that no matter who are we loving either it is of the same sex or no merely manifest our being human.
Love is a feeling wherein we care so much for someone over ourselves. We give high regard to the person that we are loving because of so many reasons that we cannot even chose which is which that made us act so dearly towards them.
In fact, they say that you cannot explain why you love someone because there is no definite answer to it. You just love a person because you love the person. And you cannot chose who to fancy.
Lust on the other hand is not love and does not feel like love at all. It is more of a carnal longing or the urge to be intimate with someone we fancy. The urge to have sex bluntly speaking.
As what has been said being a Lesbian per se is being human. Loving someone of the same sex does not make someone less of a human being that she is.
One has to understand that when a person loves someone of the same sex it is basically working just the same as the relationship the heterosexual couple is having.