Deborah Kerr and Robert Donat play two naive people who marry without much in common. The war breaks out and both of them enlist. (She in the Waves). Their wartime service changes them into more independent people and also adults. When the war ends, both are convinced their marriage is over based on what they know about their partner.
Alexander Korda directed this in 1945. It is also called PERFECT STRANGERS. It was quite a decent little film and treated a serious subject in a respectful way. It is the kind of movie you might like if you stumble on it, but perhaps not the sort you would rent on Amazon.