This question has become more common in recent years with the passage of laws in some states that recognize same sex marriage and unions.
The Catholic Church has always taught that this inclination is disordered.
It distinguishes the sexual orientation from sexual activity. Whether the orientation is biological, psychological, or social, in most cases it is believed to be involuntary; hence, there is no culpability merely for the inclination. The sinfulness comes not in the same sex orientation, but in the acting out of the orientation, any and all acts of same sex activity.
It is not sinful to have the same sex orientation, but it is sinful to engage in same sex behavior.
The Church still considers the orientation disordered but recognizes many individuals do not choose to have this inclination. Only when they engage in same sex activity is there culpable sin. Any and all human sexual activity, which is outside of marriage (between one man and one woman) is considered seriously and gravely sinful. Adultery, promiscuity, fornication (sex before and outside of marriage), and artificial contraception, pervert the original intention that God has for marriage, namely love (unitive dimension) and life (procreative dimension). We learn this from the book of Genesis, in which God creates male and female and tells them to be fruitful and multiply.
The Church teaches that God instituted the sacrament of Marriage, and only He has the authority to change the nature of marriage. Neither the Church nor the state has the competence to alter the substance of marriage, or the family, for that matter. Any attempts by civil governments to alter the law in favor of same-sex unions distort the true meaning of marriage, which has existed for thousands and thousands of years.