expense: "A loss for the sake of something gained; a sacrifice"
So if we take into account this above description, the original sentence can be explained as the idea of people suffering a loss (personal relationships) for sake of something gained (material possesions).
It is suggesting that some people are so concerned with material possesions that their relationships with other people (friends, family, etc) weaken and become less important by comparision.
I'm not a qualified teacher.
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