Basa-Basa-Forbids
Source: My First Cathechism
Adultery: It is a very big sin to have a sexual relation with aarried person.Jesus saqid: You have learnt how it was said: You must not commit adultery. But I say this to you: If a man looks at a woman lustfully, he has already committed adultery with her in his heart(Mathew 5:27-28)
Divorce: Whoever divorces from his spouce, for whatever reason, is running towards eternal damnation.Jesus said: What God has united, man must not divide. The man who divorces his wife and marries another is guilty of adultery against her(Mark 10: 9-10) Divorced people who live-in with another person, or who remarry under the civil law, cannot receive any sacrament.
Fornication: It is the sexual union between a man and a woman outside the sacrament of Marriage. Those who live-in, or who have only civil marriage, are also guilty of fornication.
Homosexuality: Whoever has a sexual relation with a person of the same sex will not enter into the kingdom of God. Scripture says: The sodomites will never inherit the kingdom of God(1 Corinthians 6:9-10
Premarital sex: To have sexual relation before the holy sacrament of Marriage is a sin of fornication. Jesus said: A man must leave father and mother, and the two become one body(Marj10:7). To leave father and mother implies the sacrament of Marriage.