Truth - and knowing what TRUTH TRULY IS - is vital to marriage. Truth does not mean accurate verbal description. Court testimony is different from good human relations. The Torah has enormously high standards for truth. Generally speaking we must never lie."The lip of truth is established forever but the lying tongue is gone in a moment" [Proverbs 12:19]. "Hashem's seal is truth" [Shabos 55a]. However some people pervert truth destructively and they can wrongfully hurt others very much, especially in sensitive or close relationships.
A shadchan told a guy that the girl he wanted to see would not go out with him because "he is too short." This hurt the fellow's feelings; especially since his height was not a defect, and there is nothing he can do about it anyway. When asked why she didn't use a tactful way of saying the girl was not interested or available, she adamantly said, "I speak the truth!"
In a marriage scenario, you may want to say to your wife "Tonight's dinner was terrible!" You unappreciatively disregard the fact that she worked to shop, cook and serve the meal for you. Or, you might be tempted to get cute and say, "You look terrible dressed like that. I admit it. You've discovered how to look like you've left the human race. Now can you put on some clothing instead of a potato sack, for a change!?"
It may accurately describe your feelings. But it is not truth. Truth is peace and making your spouse happy. If your spouse is dressed like a laughingstock, you can try a more positive attempt at salvaging human dignity, such as recommending a color that your spouse looks good in (one that is not the color that he/she is now wearing) or recommending that a certain suit will look fabulous with your spouse's eye-color. Keep it positive. Speak with a soft, warm tone.
The Chazon Ish told a young man that when his wife places a picture on the wall, it has NOTHING to do with the picture. The husband should not react in terms of whether he likes the picture or the location where it is hanging. If he says what he "truly" feels about the picture and hurts her, this is NOT TRUTH. What is TRULY going on? He should understand that his wife wants his love and appreciation for caring for the house.
Let's say a wife says to her husband, "Move the picture from this wall to that wall," or "Fix your clothes (e.g. straighten your tie)." The man thinks that there is no worth or merit to the statement. Regardless of what he thinks about the picture or the clothes, he has to be very careful, sensitive and detailed in doing what his wife wants. If he is not, she is going to feel unloved, unwanted, unimportant, cheap, hurt, abandoned, that she doesn't matter, and that her husband's only interests in her are self-serving. It is irrelevant that a tie, flower pot, wall-hanging or his graciously eating "seaweed supreme" for dinner seem incomprehensible, insignificant or worthless to the man. It weighs heavily on her feelings. What counts is registering heartfelt responsiveness that conveys love, appreciation and respect, not your "truth" that she is fussing over a "senseless non-entity." Correspondingly, if he values work, Torah learning or a hobby, she has to be supportive and agreeable, as long as he doesn't get too lost in his interests. If she nags or criticizes his interests, he will get irritated...even if her putdown is how she "truly" feels. Let them communicate, but there has to be room for each other's needs and the truth which is under the surface. Speak nicely, with sincerity (when you're phony, it doesn't work).
What is truth? Truth is the will of G-d. Generally, G-d does not want fights, anger, divisiveness or inflicting of pain. Generally, G-d wants love, respect, pleasantness, peace, midos and good deeds. Remember that Aaron was beloved for making peace between friends who had a fight by saying to one that the other feels so much love and feels so bad about the dispute. When the first friend was appeased Aaron ran to the second friend and also said that the first one feels love and feels very bad about the argument. The friends ran to eachother, hugged and made up. The friends never said the things Aaron reported. Truth meant love and peace, doing good and saving from bad - not accurate reporting.
The Torah (Genesis 18:10-13) reports that Heaven sent three angels to visit Avraham when he was 99 years old. They told him that he was going to have a son in one year. Sara, his wife, who was 89, was right behind and heard. She laughed within herself and said that HER HUSBAND was too old to have a child. G-d came to Avraham and said that Sara said that SHE was too old to have a child.
If G-d were interested in defining truth in marriage as "accurate reporting," He would have quoted to her husband what Sara TRULY said: her husband is too old to have a child. Sara called Avraham old, and Hashem did not want Avraham to hear that. Marital peace is so important that G-d himself changed Sara's words so as to not in any way diminish peace between Avraham and Sara (Yevamos 65b).
Consider from this how important marital peace is. Here we have a husband and wife who were 99 and 89 years old. They'd been married 60 or 70 years. On top of that, they were uncle and niece - family, even before marriage. Didn't they know eachother already? Didn't they have a secure relationship already? Even so, G-d Himself, with their deep and established relationship, manipulated the report so as to be in accordance with ULTIMATE TRUTH, G-D'S TRUTH: LOVE COMES BEFORE PAIN AND PEACE COMES BEFORE ACCURACY, IN DEFINING MARITAL TRUTH. Important note: this article does not mean to suggest that one may tell lies. It means that sometimes people lose sight of true priorities or principles and they use "truth" perversely to suit themselves or to hurt others. We must always be on guard to apply G-d's definition of truth, and to ask qualified rabbinic authorities when questions come up.