Best way to initiate a serious discussion?

What is the best way to get through to an ADHDer if trying to convey that there are really serious issues that need to be addressed?  Is face-to-face better, or is it more effective in written form (a letter printed out and handed to them, not email) to give them a chance to sort through emotions/defensiveness/impulsiveness before having to respond?

None of the issues are new; we've discussed them several times but there hasn't been any lasting change.  As I prepare to go home from my deployment, I'm establishing better boundaries than I had before I left.  I want him to know that I want to rebuild our marriage, but that it will take hard work from both of us, and there are things that MUST change to keep our marriage alive.

I'm not planning on having this discussion or delivering the letter until after I get home in a few weeks.  From past experience I know that addressing it from afar isn't the best course of action.

Any advice (from ADHDers and non's)?