No, US is not going to sit in Afghanistan forever and when the tide turns Pakistan will want sympathetic people in its border region.
And in all that time we support a mosnter who is killing our own people, our own armymen? Who knows for how long US remains in Afghanistan?
Remember Afghans do not want US in their country either or us, better to help them fight their enemy (which appears to be our friend to them, who really create this jihadi headache for us time to time, certain rogue groups of Taliban can be tolerated but not a whole mainstream Afghani regime of Taliban going against Pakistan). This is no easy game to play.
US has long interests in Afghanistan, if all they wanted was to oust Taliban (so called objective) they'd have gone end of 2002/03. Whether Afghanis want US out of their country or not we cannot destroy our own nation, we cannot let world declare our country as terrorists/terrorists-haven, this is detrimental to our existence and our society.
You also should remember Afghanis have been anti-Pakistani since birth of Pakistan.