keep (one) sweet
To do nice things for one in order to maintain their loyalty or to elicit some benefit from them in the future. She isn't the easiest person in the world to work for, but she keeps us sweet with a big fat bonus at the end of the year. He's been keeping the superintendent sweet so that he'll get a favorable review at the end of the year.
keep somebody ˈsweet
(informal) be pleasant and nice to somebody, so that they will treat you well: I have to keep my mother sweet because I want to borrow the car.