The relationship between the United States and Pakistan reminds me of two drug addicts whose co-dependency put them on a mutual path to self-destruction. And like drug addicts, they enable each other in ways that feed their respective addictions: Pakistan gets money to fund its military and line the pockets of its politicians; and the United States-led NATO force gets a secure base in order to eliminate terrorism in Afghanistan (which it hasn't done despite being in that blight of a country for nearly a decade).
One can argue who needs the other more, but I would place my bet on the United States. For the United States, Pakistan is the only game in town. Iran is not an option; and the central Asian republics are unreliable. This dependency was brought to light when Pakistan closed its border to NATO resupply columns after its sovereignty was violated by NATO jets. The United States couldn't do anything about it except to agree to work it out with Pakistan.
What would happen if, for example, Pakistan got a backbone and told the United States to take a hike? Meaning, no use of Pakistani territory-- air, land, or sea-- to support operations in Afghanistan. No cooperation. No sharing of intelligence. No troops in FATA or Waziristan. No diplomatic or political support. Nothing whatsoever! This scenario is wholly plausible if the Pakistani government gave a shit about their country.
But they don't