"he asked hypothetically where the line is between knowing and not knowing? How can one ever hope to know what information to give and what not to give? After all, if you have agreed to talk about it, how can you ask what is too much information? At what point does a partner who doesn't want to know all of a sudden care what is happening? The line is pretty thin I think... the tidal wave of information at that point is on the verge of becoming a tsunami."
With non-spouse or secondary relationships, for me, that "line" is the point at which what I don't know can impact me negatively (affect my time, put me into awkward situations, etc.). It is, unfortunately, a line that the secondary needs to identify and be aware of, because I don't have the information necessary to protect myself. The difficulty I have with "don't ask, don't tell" so far, is that I keep learning things about my main secondary "the hard way," the painful way. Yeah... I don't like "don't ask, don't tell." The only person I can really trust to protect me from the negative impact of things is Me.