Your friend can manipulate in many ways: guilt-inducement, threats of abandoning you, threats of self-harm, yelling, physical aggression, isolating you, pouting, interrogating you, etc. It may be obvious; it may be much more subtle. You might be told that it's really love, but deep down you know that's not the truth. If you see glimpses of controlling actions now, it's fair to say they will likely increase after marriage.
Christian men can hide their control behind headship. Yes, the Bible does speak to the place of headship in a husband (Eph. 5:23), but it's not about domination or manipulation. Jesus is given as the model for headship, the one who came not to be served, but to give his life for you and me. Headship has more to do with servanthood than with being "in charge." It's more about his responsibility before God to encourage the relationship positively than about him demanding his own way. The mutual submission that is stated in Ephesians 5:21 provide a safeguard against marital headship from being used as a club.
Is she able to submit to a husband, or does life simply need to go her way? When a woman has experienced over-control, abuse, or harshness in her years growing up, submission may not come easily. Even when headship is carried out in a loving balanced fashion, she may fear that it will turn into domination. There may still be some wounds that need to be addressed.
"I'm sure she was just stretching the facts a little bit." "He lied to me so that I wouldn't be hurt." It's easy to minimize or overlook instances of dishonesty in a relationship. But lying is often a pattern that pulls the rug out from under a marriage. If you can't trust a person's words, what can you trust about them? Lies that we're aware of are often the tip of the iceberg. We want to trust our friend. But when we find an instance of dishonesty, it causes us to wonder what else has been stretched or distorted
"Truthful lips endure forever, but a lying tongue lasts only a moment." Proverbs 12:19. What greater picture of the outcome of honesty can we find? Like most sin, lying has momentary purpose, but it leads to destruction. Does your friend have a reputation that his/her words can be trusted? Is truth compromised for gain, impact, or convenience?
"She doesn't drink like that too often." "Oh, he told me he's not going to look at pornography anymore." When we want a relationship to work, it's easy for us to rationalize away the red flags. Chemical dependency, sexual addictions, food addictions, etc. will gnaw at the very fabric of a marriage. If you're seeing the problem now, don't simply accept good intentions; the addiction will likely intensify. Your friend likely needs help physically, emotionally, and spiritually to experience sobriety in whatever arena of struggle. People can often "white knuckle" an addiction for a period of time, but when stress, frustration, hurts, and fatigue set in, it's easy to return to old patterns. In most instances, the addiction is not primarily about the "substance," whatever that may be, but about the pain underneath that needs to be addressed.
There's no guarantee that a person will not return to a former addiction, but if there is at least a year of consistent sobriety, chances diminish significantly. Again, the difficult question remains; if I were not saying that something needs to be done about this addiction, would my friend be pursuing help?
Inability to Apologize
We all mess up, no one is exempt. How does your friend admit when wrong? Or should I ask, does your friend acknowledge his/her mistakes? We don't want to be wrong, but dealing with it when we are goes a long way towards establishing a healthy marriage.
People may tend to struggle more with admitting mistakes when they've grown up around critical people. For some, Paul's words in II Corinthians 12: 10, "For when I am weak then I am strong," is experienced as, "For when I am weak then I am worthless."
Writing out an apology may be easier than saying it. Practicing with a small matter may make it easier when the offense has a greater emotional impact. But saying "I'm sorry" needs to happen for a relationship to thrive.
Unwilling to Get Help
If your friend is not willing to go to counseling if you marry and can't resolve an issue together, don't marry him/her. I know it may sound self serving since I'm a marriage and family therapist, but it's true. It's not merely about one's willingness to meet with a counselor or pastor; it's about one's willingness to grow, to be open, and to learn. A person might agree to it now, but conveniently has a change of mind after the "I do's."
There are often two reasons why people will avoid counseling. One, they know at a deeper level that the way they are approaching life and the relationship is not healthy. If it stays an issue just between the couple, one may succeed at convincing the other that there really are no problems, or if there is, the problem is the partner's. On the other hand, if they meet with an objective counselor, it's going to be a lot tougher to keep an unhealthy perspective alive. Secondly, a person may know that there's pain that needs to be faced, but it may scare the person half to death to do so. "If I meet with a counselor, I'll probably have to face some pains I've successfully avoided until now." Of course the price of not facing the pain is a lot more costly than facing it.
What current evidence would lead you to believe that your friend would be willing to get help when married? Is he open to learn from others, or does he know it all? Does she have a humble attitude, or is there arrogance in her tone and words?