Strong’s Concordance gives us the originaldefinitionofporneia. 1) illicit sexual intercourse. a) adultery, fornication, homosexuality, lesbianism, intercourse with animals etc. b) sexual intercourse with close relatives;
Now for my 1 centavos worth.
Catholics believe (or are supposed to) that marriage is not a contract but a covenant, just like God’s covenant with the Israelites. Sometimes their is language in a contract that allows one party to walk away, therefore dissolving it. Not so with a covenant. Just as many times the Israelites turned away from God in the OT, He still kept His covenant with them. So it is with a Catholic marriage. Even if my spouse were to cheat on me, I am still called to keep my end of the covenant. This is why marriage is never to be entered into lightly.
I have heard both sides of the argument that Jesus says it’s okay to remarry when one side has been unfaithful. The word porneia is a catch-all for many things. It is quite possible that Jesus’ was talking only about a few of the many items that porneia covers. The Greek perhaps did not have the specific words the writer needed ( Petros Petras anyone?). I would like everyone to prayerfully consider this passage, eespecially verse 10:
there.3aSome Pharisees approached him, and tested him,saying, “Is it lawful for a man to divorce his wife for any cause whatever?”4**bHe said in reply, “Have you not read that from the beginning the Creator ‘made them male and female’5cand said, ‘For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh’?6So they are no longer two, but one flesh. Therefore, what God has joined together, no human being must separate.”7**dThey said to him, “Then why did Moses command that the man give the woman a bill of divorce and dismiss [her]?”8He said to them, “Because of the hardness of your hearts Moses allowed you to divorce your wives, but from the beginning it was not so.9eI say to you,**whoever divorces his wife (unless the marriage is unlawful) and marries another commits adultery.”10[His] disciples said to him, “If that is the case of a man with his wife, it is better not to marry.”11He answered, “Not all can accept [this] word,but only those to whom that is granted.12Some are incapable of marriage because they were born so; some, because they were made so by others; some, because they have renounced marriagefor the sake of the kingdom of heaven. Whoever can accept this ought to accept it.”
The reason the Apostles say it would be better not to marry is because Jesus has basically just said to them that there are no reasons for divorce (of a lawful marriage).
p.s. Now playing devil’s advocate He also says whoever can accept it ought to accept. You could say “Lord I do not accept it.”