You and I go way back, have I ever let you down?
It's from a dialogue from House of Cards. Frank was trying to persuade someone to give him more time to deal with an issue at hand. My guess is "go back" means the two of them understand each other pretty well because the have a long history, and in this case the "someone" understands the capability of Frank from the past the have been through. Is this correct?
Best Answer
When used between two persons, go back means having known each other for a length of time (sense #2.a). Putting way simply implies a longer duration.
So, here, it means that those two persons know each other for quite a long time.