For the love of Pete, can we just pick a restaurant and stop searching? I am hungry.
This phrase and phrases like for Pete's sake are euphemisms for the phrases for the love of God/Christ or for God's/ Christ's sake and hail from a time when those phrases were considered blasphemous. Nowadays phrases like for the love of god are commonly used, but the euphemisms are still used.
Why Pete? Most likely it is a reference to the catholic Saint Peter.
Other phrases with similar origins are: Zounds! (archaic British slang), is a contraction of christ's wounds, oh my goodness and oh my gosh for oh my God and gosh darn it.