Being a Catholic Christian, I believe that marriage is only valid between a man and a woman, and that only married couples should have sex.
Having said that, I don't think that having the homosexual tendency in your thoughts and feelings is any worse than heterosexual thoughts and feelings. Indeed, having lustful thoughts toward anyone who is not your spouse is sinful.
There is no discriminatory standard against homosexuality in the Church, or there shouldn't be. We are all human, and we all have lustful feelings towards both sexes at one time or another. There is the same standard for all humans.
I consider homosexuals having sex outside of marriage the same as heterosexuals having sex outside of marriage. I am tolerant and loving toward people who do it, although I don't personally think it's the best thing.
Homosexuals have to face something very difficult, as we all do in our own way. We all have our own issues that make it hard to be human. Homosexuality is just another part of being human, and it's clear that it occurs naturally. As long as it's not acted on, I don't see this particular tendency as being bad.
Some people are not called to marry, and Paul even discourages people from getting married(if it can be avoided) quite emphatically, as in 1 Corinthians 7. So it is quite an expectable(although difficult for most) thing according to Paul for people to just go through life celibate.
The problem comes in where everyone wants to have sex, no matter what orientation. And so people act to get what they want without doing it properly(i.e. without marriage). It's the same problem with everyone.
A close analogy is if a friend wants something in your house that belongs to your parents, but you don't feel like waiting to ask your parents, so you decide to give it and hope everything works out ok.
I believe God owns our bodies, and we should get permission from Him through marriage in the appropriate way before we can give our bodies to someone else. All this, of course, precludes some belief in traditional Christianity.