Thomas and Judith both home after the park

After the meeting between Judith and Georg in the park, the first time we see Judith and Thomas again is in their house/office. The next time is at the dinner table at the birthday party.
The scene in the house is weird: Thomas lying on a couch (pretending to sleep), Judith entering that room, starting to say/ask something ("Thomas ...") but stops as she thinks he is asleep. She touches his hair and goes off. After she is gone he opens his eyes and there is a heavy sigh.
That's it!

Any further reflection/reaction on the encounter in the park is postponed till the next evening! So why is this scene in the movie? It took me a while to get to an acceptable interpretation.
What I missed was any action by Thomas. After all, your wife is acting strange, she goes out with an strange excuse, she has a secret meeting with the man you hate most in this world. As a final step he puts his arm around her and leads her to ...
And when she comes home, hours later, he doesn't say or do anything but sigh! That's exactly the message!