I can't stress how important it is to keep your composure.

Remain calm and try your best to keep your emotions in check if/when you have this discussion.

Emotions + decisions = bad news

Do not get sucked into an argument or fall into the trap of constantly defending yourself.

Maybe it would be wise to be a little more quiet and sit back and see where the discussion goes.

Again, if you are unsure of anything or you don't feel comfortable committing to something, tell him you need some time to think about it.

Don't stand still.