He needs to leave her in order to investigate further in the black mass matter, so he needs to leave her newly wed wife,eventhough he loves her very much he must do this, and by the way he communicates with her you can see that he is a loving husband.
It can be discerned that Goodman Brown is a
loving husband because of how he calls his wife “My love.” Too, with the
words, “of all the nights in the year, this one night must I tarry away
from thee,” readers can discern because he says “must” and not
something like “want,” he must be away from his wife against his will,
which paints the image of a loving husband—one who dislikes the idea of
have having to be away from his wife even just one night.
I think the main theme that is best expressed in "The Gift of the Magi" is love. The reason why I think this is because Jim and Della were willing to make each other happy and they showed that the wealth of love makes up for the poor.