Der Blaufuchs (1938)

Ilona, the bored wife of an easily distracted professor, falls in love with his friend Tibor, a world-traveler and ladykiller. Although she pursues him, he declines to take advantage of the situation, because she's married to his best friend. Only after her husband shows an interest in a co-worker is it possible for a happy ending to take place for the two new couples.