One of the tests of friendship is whether anyone is keeping accounts.
Once a friend begins to keep accounts, even if the relationship continues in some form, it has become a commercial or semi-commercial relationship, which is very different from a friendship.
Thus, many supposed friendships (among them many boyfriend-girlfriend relationships) are actually commercial enterprises, in which one side gives the money, and the other side pays in behavior, influence, or some other currency.
When one friend begins to calculate and compare what he gave and what he received, when one demands, or even thinks about, some return for his gifts—not only monetary value, but a kiss or a smile—the friendship has died and has become a business relationship.
–Rabbi Adin Steinsaltz
From "Friends," an essay in Simple Words by Rabbi Adin Steinsaltz