Is Marty a virgin?
He coudn't have lost his virginity while serving in either WWII or the Korean War because there was no allusion to him having served in the Armed Forces.
He seems to much of a self-conscious gentleman to have purchased a woman's embrace. Plus his Catholicism would have condemmned visiting a hooker.
So, if you look at the film in the light that he is a virgin, it makes much more poignant sense.
Up until the point of meeting the teacher, he had been married to his mother.