The question of how do you detach and act all happy when inside you are falling apart is one of the difficult ones to master. It is one I struggle with every day. My H left 6 months ago and each day I want to send him a text saying "I miss you" or "I hate you for doing this to me" (it really depends on what has been going on in my mind). I think it is a matter of stopping yourself when the thoughts come, taking a breath or two, then getting on with whatever you were doing before the thoughts filtered in.
It is more difficult when you actually have to interact with your spouse, which in my case is often, because of the kids. I try and treat him like a casual work acquaintance. Friendly but not overly familiar, so non children/logistic related topics tend to be casual pleasantries, weather, daily commute etc. Nothing too personal. It is hard to do but with practice it can be done. When he leaves I go and sit in my room for five minutes, have a cry, wash my face and come back down to the children. Although frequent, these interactions are fairly short in duration, because he feels as awkward as me. 16 years together, and your reduced to talking about the weather. It is safe ground though. I hear you, putting on a fake smile is heartbreakingly difficult at first, but I am hopeful, that it eventually just becomes habit.
