Homosexuality should not be singled out as a sin itself, because heterosexual couples can sin by having sex outside of marriage, married couples can sin by coveting another person or even looking at lewd media or pornography.
Its not by our regular emotions, feelings or even tendencies that lead to sin, but the lustful act itself which will be talked more by Fr. Fernando below
Chastity is Purity of heart
"Shower, O heavens, from above, and let the skies rain down righteousness, let the earth open , that salvation may spring up"
Uncleanness of heart produces insensitivity to the things of God but with pure of heart spring joy, the ability to see the divine trust in God, sincere repentance, recognition of ourselves and our sins, great love of God and other people
Read Matt 15:2,7-8
The whole man is defiled by what happens in his heart, evil desires and intentions, envy etc are external sins which our Lord enumerates, even if they are committed internally in the sinners heart. Jesus describes as blessed and happy those who guard their hearts
If we don't try to guard our heart then otherwise we always tend to attach themselves in the wrong way to people and things. Among all the aims of our lives, there is only one, to go to heaven, and we do this to live our individual vocation to the full
Mat 5:29 -30
Our Lord means anything that at given moment seems indespinsibleby precious and valuable, Sanctity, salvation ones own and ones neightbor comes first
The things we need to abandon or cut out of our lives can be all different sorts. They can be even good things in themselves but self feed our egoism or a failure to rectify our intention which has then turned into obstacles in our sanctification. We need to guard the small whims that result in failure of complete control. St Augustine notes "the sea comes through leaky places and little by little fills the hull of the boat. Unless expelled the boat goes down..need to imitate the sailors that pump the water out even though it continues to fill with water, because the weak points of our human nature are always there; and you will have to have man the pumps again"
Love of frequent confession and persistence with the daily examination of conscience help help us to keep our souls clean, even of our daily obvious daily weaknesses
If our hearts are pure. then we will know how to recognize Christ. in the intimacy of silent prayer, in the busy middle of our work or any other other daily events., but if we lack inner purity the clearest signals will mean nothing to us and will interpret them wrong
Let us contemplate God the father, the Son and Holy Spirit and well the Blessed Mother also, then we shall now God as he knows us, directly face to face