A man in the congregation where I preach committed fornication with a woman who is a "pastor" in a denomination. She became pregnant. Should should he marry her, even if he does not love her?
First, let us make clear that the pregnancy is a distracting issue. What should or should not happen is because the man had sex with a woman to whom he was not married. The pregnancy is probably what led to the discovery of their sin, but it is not in itself a sin. In other words, even if a child wasn't produced how this problem should be handled does not change. What it does create is additional responsibilities for the consequences of his sin.
When dealing with sexual sins, I found that being blunt is a better way to handle issues. I don't use crude terms, but I don't disguise what I am saying in indirect phrases. Paul stated, "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God" (I Corinthians 6:9-10). Define all the terms with the man involved and let him know that his choice will prevent him from reaching heaven unless he corrects the situation.
While we do not live under the Old Law, it is sometimes useful to learn how matters where handled under that law.
When a person committed adultery, that is when one or both of the people involved were married but had sex with someone who was not their spouse, the penalty under the Old Law was death of both parties. "The man who commits adultery with another man's wife, he who commits adultery with his neighbor's wife, the adulterer and the adulteress, shall surely be put to death" (Leviticus 20:10).
In the case where the woman is engaged to be married, there was consideration as to whether it was rape or fornication. "If a young woman who is a virgin is betrothed to a husband, and a man finds her in the city and lies with her, then you shall bring them both out to the gate of that city, and you shall stone them to death with stones, the young woman because she did not cry out in the city, and the man because he humbled his neighbor's wife; so you shall put away the evil from among you. But if a man finds a betrothed young woman in the countryside, and the man forces her and lies with her, then only the man who lay with her shall die. But you shall do nothing to the young woman; there is in the young woman no sin deserving of death, for just as when a man rises against his neighbor and kills him, even so is this matter. For he found her in the countryside, and the betrothed young woman cried out, but there was no one to save her" (Deuteronomy 22:23-27). Because of a lack of witnesses, the woman is considered innocent, but the man is considered guilty. If others could have known, the lack of resistance by calling for help is taken as proof that the sexual act was consensual and both the man and the woman lost their lives.
Bringing up these two examples is important, even though adultery is not usually considered a crime punishable by death these days. First, the marriage covenant was taken very seriously, even by those engaged to be married. Second, the man is always held responsible when an act of sex takes place.
The final case is when a man has sex with an unmarried, unengaged woman. "If a man finds a young woman who is a virgin, who is not betrothed, and he seizes her and lies with her, and they are found out, then the man who lay with her shall give to the young woman's father fifty shekels of silver, and she shall be his wife because he has humbled her; he shall not be permitted to divorce her all his days" (Deuteronomy 22:28-29). The woman's father did have the right to refuse the marriage. "If a man entices a virgin who is not betrothed, and lies with her, he shall surely pay the bride-price for her to be his wife. If her father utterly refuses to give her to him, he shall pay money according to the bride-price of virgins" (Exodus 22:16-17). Even when the father refuses, the man is still held responsible for his action. He was required to pay the bride-price typically given to marry a woman anyway.
Hence, when talking with a man who has committed a sexual sin, I ask him why he did it. I don't let him get by with "I don't know" ("Do you often do things without knowing why you do them?") or "It just happened." ("Explain to me how it just happened that your pants came off, her skirts were lifted, and some how your penis ended up in her vagina. Somehow this doesn't sound like something that can accidentally happen.") I don't tell him what to say, but I don't let him make excuses for what he did. My goal is to get him to own up to his responsibility for what he did; just as Nathan was able to get David to admit his responsibility in committing adultery with Bathsheba (II Samuel 12:1-14). Until there is a willingness to face the reality of the sin committed, there can be no righting of the wrong.
One of the things I noticed in your question that I would not let go by is your statement that he doesn't love her. I would ask in very blunt terms, "Why are you putting your penis in a woman you don't love." It indicates there is more than just the sin of fornication that must be dealt with. It appears the man sees women as objects to be used and thinks only of satisfying his own sexual appetites. Such a man has a worldly focus that will prevent him from reaching heaven. There are several warnings about people who are self-seeking or who have selfish ambitions (Romans 2:8 ; II Corinthians 12:20; Galatians 5:20; Philippians 2:3; James 3:14-16). Peter warns, "The Lord knows how to deliver the godly out of temptations and to reserve the unjust under punishment for the day of judgment, and especially those who walk according to the flesh in the lust of uncleanness and despise authority. They are presumptuous, self-willed" (II Peter 2:9-10).
Then there is the question, did she know he didn't love her as they were engaging in sex? Most likely he will admit that he led her to believe he did love her. So on top of fornication and selfishness, we have a man who is willing to lie to get his sexual desires satisfied.
Only until he is thoroughly convinced that God would be justifiably angry with his choice and that he is willing to accept that he was responsible for these sins would I then talk about repairing the damage he committed. Start with II Corinthians 7:9-11, "Now I rejoice, not that you were made sorry, but that your sorrow led to repentance. For you were made sorry in a godly manner, that you might suffer loss from us in nothing. For godly sorrow produces repentance leading to salvation, not to be regretted; but the sorrow of the world produces death. For observe this very thing, that you sorrowed in a godly manner: What diligence it produced in you, what clearing of yourselves, what indignation, what fear, what vehement desire, what zeal, what vindication! In all things you proved yourselves to be clear in this matter." Spend time going over all the phrases in verse 11 because this defines what constitutes true repentance. In particular, discuss what it is that he can do to clear the reputation of himself and the church where he claims membership.
One of the things I don't know about is her situation. Does she have a reputation of having sex with many men? Or is this incident damaging her reputation? What is going to happen to the child, who is innocent of the sin committed by this man and woman?
From what I understand, in your country a man who gets a woman pregnant is expected to marry her. It is a reasonable requirement, even if he doesn't like the idea because the child needs a mother and father to raise him. Even that is a step down from Israel's laws that simply stated that a man was expected to marry a woman with whom he had sex, regardless of whether a child was produced or not. Unfortunately, in my country we have lost that sense of responsibility and children are being born out of wedlock in record number. At least our courts retain the sense of decency to require that a man who fathers a child to be financially responsible for his child until they reach adulthood.
The important thing is that in the sight of God and of man, this man accepts the responsibility for his sins and faces the consequences of those sins. No one made him have sex. It was his choice. But that choice brings with it responsibilities that he must bear. There are solid reasons why God said sex was only for the married, he will live many years learning these reasons the hard way.