It's reductive to say that the Catholic Church merely condemns gay sex. They also do not allow gay people to get married - which is the difference between their stance on pre-marital sex. There is no way within the framework of Catholicism that one can live as a gay couple, completely equal in rights to heterosexuals. It is Catholic Church doctrine to discriminate between heterosexual and homosexual couples - and if that discrimination doesn't read as condemnation to you, the church also literally condemns people to hell who disagree.