What makes a friend?

In high school, I had this idea of friendship. If you were friends with me, you kind of had to endure this kind of tough love friend. I skirted the line of judgementalism- I imagine growing up very right wing Christian didn't help that.*

Since then, I've loosened up. I think. I tend to temper my own opinions with a dose of- well, I was trying for sensitivity. I bite my tongue alot more. I think more about what I want to say and what I don't. I consider the pros and cons of things I want to say. I have very select friends with whom I am 100% honest, and most of all just my husband. Because most people don't actually want to hear what I really have to say. Which is fine, I don't think I'd always want to hear everyone's totally honest opinions either.

I guess the question for me remains: Where, in friendship, is the appropriate line of honesty and, um, tact and sensitivity. One would argue that you can be honest with tact, and I 100% agree. However, there are times that no matter how much tact you use, some people and in some situations do not want to hear the truth (myself included, at some times, if truth be told. no pun intended). I am still working on when to be honest and when to keep my big fat mouth shut. I tend to be opinionated (those who know me are laughing their asses off right now) and I need to work on keeping my opinions to myself a bit more.

So, I have this friend. And she told me that some comments I have made recently were insensitive and unsupportive. One of them probably was. I don't remember the rest and I wans't made privy to that information. Apparently I don't get details on what I've done to offend, I can just guess and hope that in the future I don't make the same mistakes again. There are some things I can guess at. My problem is? That I've done ALOT of biting my tongue with some of these things, and for someone like me, you can only bite your tongue for so. damn. long. Sometimes things just slip out. I swear, I didn't mean to hurt. If was allowed to talk to her right now (she's asked for some space), that's what I'd shout. I'd never have wanted to hurt. I love the people I choose at my friends and it hurts me when I've hurt them. I just want to make it better, and it's hard for me that I'm not being allowed to try. I wrote an apology e-mail and was more or less asked to leave it alone, and I will. While I don't understand it- my style is to have a problem, talk about it, and move on- I will respect it.

My question is this, and really, if you're reading, I'd love an answer. Even just your own opinion would be great: when is honesty too much? If you say it with tact (and I'm not proposing I always manage that) and love, when is honest being a friend and when is it offensive?