I would like to question the WT interpretation of "marrying only in the Lord". I maintain that marrying only in the Lord is based on what Jesus said about marriage. One does not go out and steal anothers marriage mate. He does not commit adultery. He doesn't rob the cradle for selfish reasons.
Paul based his advice on marriage on what Jesus taught. That is what he means marry only in the Lord.
He also said if one burns with passion then he should get married. If no one is available in his environs, then why can't he search elsewhere?
He said also, Do not become unevenly yoked with an unbeliever. This does not mean that one cannot have a partner in business or other associations and it also includes marriage. Paul said do not be unevenly yoked. If an old man marries a young girl, even if they are both JWs that is being unevenly yoked. If a business partner, is a crook, then associations with him is being unevenly yoked.
What is a believer? Do unto others as you would want them to do for you. Many people in the world believe in Jesus words. JWs say that only they are believers, the rest of the world is bird food.
Paul also says that if one is married to an unbeliever he should not leave that person. If that is so, then why can't one go and find a kind, good supporting marriage partner and get married.
There are a number of cases in the Old Testament, where people were married to non Jews. Moses for one. Solomon had many foreign wives.
I have written this quickly, I hope you can grasp what I am trying to say.