Victor First off, homosexuality isn’t a sin.
Homosexuality IS a sin. To be a homosexual or to have the desires are not sinful until one acts on them. This is Church Teaching. See CC 2357-2359. Note that it is referring to the acts themselves and not the individual. Also notice what it says about the individual. You may also want to check http://www.catholic.com/thisrock/2004/0407sbs.asp from Catholic Answers