When Franz gets home from his trip, he wonders if his wife is OK. He goes home to find her there.
She tells him that she's fine, and has no problem with him leaving to move in with Sabina.
Franz is disappointed. He stayed married to Marie-Claude all this time because he thought she couldn't handle him leaving her. And now she seems to be fine with everything.
He gives his lecture that afternoon and then goes to Sabina's place. No one comes to the door when he rings. He feels he can't go home, so he takes a hotel for the night.
The next day he looks for Sabina again and finds that she's left town. The movers refuse to give him her new address. So Franz rents himself a small flat.
Franz moves on with his life and starts to forget about Marie-Claude.
Eventually he realizes that, contrary to expectations, he is not unhappy. He doesn't need Sabina's physical presence. Instead, "what was important was the golden footprint, the magic footprint she had left on his life and no one could ever remove" (3.9.18). Sabina helped him sweep everything he didn't like out of his life.
In fact, Franz had always preferred the unreal to the real. Now that he lives with Sabina's ethereal presence, he doesn't have to worry about losing her love.
His newfound independence makes him very attractive to women, and one of his students falls in love with him.
Franz ends up in a relationship with the student. She loves and admires him the way he once did Sabina.
He decides he wants to marry her and goes to his wife to get a divorce; she refuses to give it to him on the grounds that "love is a battle" and she intends to keep fighting (2.9.29). Franz tells her he doesn't feel like fighting, and leaves.