First of all, let's separate sin and scriptural truth right out of this discussion. Aside from those, I think there are a lot of "truths" that we hold on to very tightly--our preferences, our biases, and our prejudices. I don't think withholding these is necessarily a bad thing. In fact, sometimes I think it can be the wisest thing to do...to keep quiet on those.
I don't think I can always handle your "truths" either. I don't know if I want you to tell me if I look fat or am having a bad hair day or if the sound of my voice gives you the same feeling that someone scratching their nails on a chalkboard gives you.
Truth and honesty should build up people and relationships and most of all glorify God, and should not be welded as a weapon. I taught at a women's retreat a few years back. The topic for the entire weekend dealt with authenticity. A few months later, I was talking with a woman from that church and she had been dealt a hurtful blow by another woman's remarks. The woman topped off the remarks with this comment, "Well, you know Kathy told us to be authentic." Obviously, nowhere in what I presented was there an encouragement to use authenticity as a means to "take down" another person. If anything, the encouragement was to be introspective and honest with ourselves, our motives, drives, etc.
Timing is important to our "truth" telling. We've all seen this played out a million times in commercials and sitcoms. The wife is standing in front of the mirror, all dressed up for a big night out and asks, "How do I look?" I am a firm believer in "not asking the question if you don't really want the answer", however, I also think that timing is an important ingredient in sharing truth, especially difficult "truths". And being loving....timing and being loving are both important.
I think intimacy has another thing to do with transparency. I am not as transparent with people that I am not as close to. For example, I might use a certain palindrome to tell a sister-friend that her top is too low cut. However, I would most likely not say that to a stranger.
Do I always tell the "truth" in all my relationships? No, I don't think I do. I am blessed with a quite a number of close, intimate friendships. Relationships forged over time. These friends know the best and worst there is to know about me. Not all my information is available to everyone. Nor do I think it should be.