Alright, so, my two cents as someone who's going to a Catholic school. Be warned, it's a Jesuit school, so this is likely to come from the liberal side of Catholicism.
Official catholic church doctrine, IIRC, is that homosexuals are human beings and worthy of as much respect as any other human being. They frown upon homosexual ACTS, but not on the person performing them.
Now, my view.
I think that if we believe in Jesus, we can recognize that Jesus was a radical. He ministered to the lepers, spoke with the women, and spoke with the foreigner, all of which were considered extremely radical behavior in his time. He came to call everyone, and that includes people who are different from us, be it that they are homosexual or heterosexual or bisexual or whatevs, black, white, whatever. He came for everyone and died for all of our sins, not just those of individual groups. As such, we are all human, and we all deserve to be treated as such.
Now, to the behaviors/actions themselves, and here I deviate from church teaching: I believe that the person has supreme choice over what they do, and I try not to judge them for that. I do not see homosexual behavior or sex-changes or whatnot as evil or sinful: they are an individual choice. If you feel called to it, then follow that calling: everyone deserves to be happy, and if you feel uncomfortable in your own body or in relations with the opposite gender that detracts from your happiness. Do what feels right, as long as you do not hurt others in the process.
What do you think homoromanticism? Homosexuality itself could be considered a sin due to the fact that gay sex does not serve reproductive purpose and thus is just lust. Which begs the question about whether or not being romantically attracted to a person of the same sex while staying virgin would be a sin?
I still have to find it, doing some searches, but I seem to recall that the catholic church does not believe that to be sinful. However, individual catholics still might, and certain Protestant groups seem to espoused that opinion.
Homosexuals can no be married because marriage is the holy matrimony between a man and a woman
Marriage as a means of connecting people as husband and wife, however, has existed in cultures all over the world outside of the spread of Christianity. As such, I believe that people should be able to be married in the eyes of the law, if not in the eyes of a church.