We can always understand everything about the other - the whys of things they do anymore that they understand or "mis"understand our stuff. If writing things on a board is usual - then just remember to put your stuff on it too and leave it at that. Your other option could be to let her know what you saw and say "sorry I forgot to write down where I was", and let it go. Altho, she may have something to say to you and that gives you the chance to listen to her viewpoint without getting into an argument. Nice 180? Just a suggestion.
Detachment sounds a bit difficult - (isn't it though) - I was going to remind you that detachment doesn't mean you ignore emotions or don't have them - the goal is as you say - to control what you do with them. When you feel emotional - are you able to identify what you are reacting to? Here's an example, when I feel anger -I ask myself,"what do I think is wrong in this situation?" Then I begin to problem solve the situation in my mind, (or my journal) sorting out what I have control over and what I don't have control over. My emotions usually follow the lead to some approp behavior or words to neutralize the situation.
I read that you do see what is working in your sitch. What do you notice that she likes about her friends? Is it the break from daily routines, going out?, talking, different activities? Is there anything brought up by her to you in MC that indicates she would like to do anything different with you? Or, have you thought about what you might to add to your life with her? or on your own? When was the last time you both tried some activity that was different for both of you?
I can read the stress in your words here - but just know that a huge difference between men and women is timing. Women take longer to process things and make changes. Everything seems to be following the course. Breathe and enjoy your night away.