nurse a grudge
Bear resentment for a long time, as in We don't know why Karl looks so angry; I think he's nursing a grudge against the family. This expression uses nurse in the sense of “foster a feeling,” a usage dating from the mid-1700s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.