Leviticus is one of the books of the Bible accepted as canonical by the Catholic and Orthodox Churches.
For sexual immorality, have you not read Genesis 19?
4 Before they went to bed, the townsmen of Sodom, both young and old — all the people to the last man — surrounded the house. 5 They called to Lot and said to him, “Where are the men who came to your house tonight? Bring them out to us that we may have sexual relations with them.” 6 Lot went out to meet them at the entrance. When he had shut the door behind him, 7 he said, “I beg you, my brothers, do not do this wicked thing! …
And Matthew 5:
27 “You have heard that it was said, ‘You shall not commit adultery.’ 28 But I say to you, everyone who looks at a woman with lust has already committed adultery with her in his heart.
And Matthew 15:
19 For from the heart come evil thoughts, murder, adultery, unchastity, theft, false witness, blasphemy. 20 These are what defile a person, but to eat with unwashed hands does not defile.”