Winter is an army fighting a 24/7/365 hot war to defend to the death the existence of a group of people who have no gratitude and give only an inkling of assistance. Sometimes Mab has to involve the protected and those plans definitely follow the omelets and eggs strategy. Also, when those soldiers get leave they want to run wild. Summer's job is to be the MP's that prevent the worst excesses in both cases.
As far as the love-hate relationships go, they're similar to families with domestic violence issues. They fight like cats and dogs but if a third-party steps in or crosses them, they both turn on them like piranha on a pig. And their relationships run a full spectrum from screaming and hair pulling to friendly professional rivals. There's a reason the Supernatural world developed such an elaborate and formalized etiquette system.