The tension existed between my char. My char really didn't like this guy at first, and even though I knew ooc that he'd just made a mistake with the trustall command, ic I had to act on his attack on me and trust him less than ever. To the extent that he no longer always provided spells at request, even for raids.

However, he was always nice to me and everyone else that I saw. He was one of the most dedicated tribs. The one that ran out and got killed (or screwed up) because of his dedication to the spire.

When this is what your char sees from someone all the time, it is not easy to continue to consider them evil. I put this to you...

A fire giant acts good all the time, what happens? Imms change his alignment to good.

Just before this happens, are you saying that my char should still be treating him as being as evil as any other fire giant? I would argue not, because his actions have shown otherwise. No reason a character closely involved with another won't spot this before an immortal makes the alignment change. It would be quite inconsistent to suddenly be best buddies just because the alignment has been toggled, whilst ignoring behavior.