Issue with playing heads-up with a "poker buddy". (long)

[daisyglaze]

If you feel bad about beating them you shouldn't play them heads up in the first place.
Hitting and running is not a solution, and I doubt they apreciate the favor you think you are doing for them by quitting after a winning streak.
Your opponents probably view situition differently then you do.
Teach them a lesson about game selection.