We talked about this a little bit a while back, but what's Marc thinking when he looks over at Kay and sees him leaving?
The next scene is the baby bath, then the road fight
I hate that. But then Marc is cleaning up the paint and can't breathe, can't get Kay out of his mind, and tells Bettina he's suffocating.
When he sees him leaving: Maybe he wanted to see how Kay was reacting?
The paint cleaning scene: at first I thought this was the moment Marc began to realize that Kay was more than an affair. But, now I think that Marc wasn't that far yet. He felt that something was not ok. He should be happy with his newborn child, the house, his girlfriend etc. but he wasn't. Then he told Bettina he's suffocating. So he feels unhappy, but he doesn't directly relate this feelings to the breakup with Kay (he still wants to think that Kay was just an affair). Maybe in his heart he knows, but people believe what they want to believe.
In another discussion thread someone wrote about Marc's breakdown after Kay told him he loved him.
Maybe that was the moment something changed for Marc. The word "love" was spoken out loud.
I'm sure Marc did love Kay. But I still don''t know when he realized this.