Yes, it is true that Pope Francis once said "homosexuality is a sin", but apparently he then qualified it to say, "extramarital sex is a sin" (as though one could somehow exclude homosexuality from extramarital sex?). He also said in another place that, "homosexuality is not a crime". It really does not matter in this context if it is a crime (though, technically, a holy society would make it so). What does matter is that it is a sin.
The desire to perform a sinful act is a sin that must be repented of. The temptation itself is not a sin, but longing for evil is evil; always. Scripture says this more times than we can count, and it clearly points to the fact that sodomy (which is the technical and less euphemistic term for "homosexuality") is sinful (Gen 19, Romans 1:26-27, 1 Tim 1:10, etc.).
There is much evidence to point to the fact that sodomy is not something originally "invented" by humanity; no, it is the work of the devil. He likes it, he encourages it, and he traps people in it. This truth is only compounded by the fact that we are told that when demons tempt people to commit sodomy, they are so repulsed by it that they cannot remain to watch. Any sin that demons are disgusted by must truly be horrid.
We are called to love sinners and help them to repent and come into the Kingdom of God. That means thieving sinners; lying sinners; idolatrous sinners; and sodomizing sinners. It is no different in the grand scheme of things: they all need the grace of God as much as we do. They all need to be guided to repent, and helped to resist further temptation. The modernists in the Church who want us to "be more accepting" and encourage "same-sex blessings" are doing the work of the devil. There is no middle road on this.