Major Ernest Pettigrew is an older, widowed gentleman. He has two romantic interests in the story, tho he is only passionate about only one of them. At one point in he is rejected by a sensible English woman, because she realizes that he is in love with the other woman (who is a different ethnicity and religion). He resists the notion that he should go for the woman he’s in love with instead of the sensible English woman.
[The major says] “At our age, surely there are better things to sustain us, to sustain a marriage, than the brief flame of passion?”
[What he is referring to in his question is the English woman’s qualities of intelligence, attractiveness, and supportiveness.]
[The sensible Englishwoman says]”You are mistaken, Ernest. There is only the passionate spark. Without it, two people living together many be lonelier than if they lived quite alone.”
Two mature people of similar interests can be good roommates. But it takes a particular someone to causes us to feel this passionate love, and it is directed towards a particular someone. The Greek work Eros (έρωτας) referes to this kind of love.
A romance starts with the spark of passion that can lead to marriage or die out after a brief blaze. Granted, it may not last forever and it certainly should not be the only quality taken into account when deciding to make a lifetime commitment. But if a marriage isn’t sparked by that quality the marriage may be very dry indeed.