First, we can know through natural reason and revelation that homosexuality as a practice is impermissible. Second, science could potentially tell us whether homosexuality is a disorder or not. However, regardless of whether homosexuality is a disorder or not, the act itself is sinful and the condition of SSA, without more, does not rise to the level of sin.
I suppose the argument could be made that homosexuality is a disorder because, at least biologically speaking, SSA is an aberration when put into context of ordinary human sexuality. Thus, homosexuality could be considered a disorder like blindness could be considered a disability.
If I had SSA, I suppose that if someone told me that I was disordered that I would interpret that as being “freakish”. However, if you were to use the term “disordered” just mater-of-factly as I had just mentioned, then I think there would be little to take offense to.
That said, I think that God may allow us our disorders and disabilities to use them as a platform for which to do great things in for God. The youth catechism does a good job (in my opinion) showing how the heavy cross of SSA could lead to great and amazing things done in for the sake of the Kingdom if those touched by SSA remain faithful to the Church. I am reminded of the blind man who was born blind so that others may know the glory of God (paraphrased, of course).
God bless you, mrld20