The Romantic Englishwoman (1975)

Lewis (Michael Caine), an English novelist with writer's block, suspects his wife, Elizabeth (Glenda Jackson), is having an affair when she goes alone on a vacation to Europe. His suspicions are confirmed when she begins a romantic entanglement with Thomas (Helmut Berger), a German drug dealer who claims to be a poet. The situation grows more complicated as Thomas reconnects with Elizabeth in England, and seeks writing advice from Lewis regarding a screenplay he is working on.