Read 2 Samuel 15:1-12.
There's a saying, "The heart wants what it wants." Often it's said in defense of something - a relationship that shouldn't be entered into, a job offer that shouldn't be accepted because of ethical conflicts, or a desire that shouldn't be fulfilled - in an attempt to pass it off as worthwhile.
The heart wants what it wants. But most of the time the heart just proves that it's a fickle thing.
All it took for Absalom to turn some of the people away from King David was a little flattery and a kiss. In doing so the Bible tells us that Absalom "stole the hearts of the people of Israel." Not that long before these people had sworn in David as their king, they aligned themselves with him, and recognized that he was their God-given king. Their hearts were his ... that is until Absalom wooed them with a little flattery and a kiss and some patience over four years.
Such is the human condition. Yes, we live in a different time and age than Absalom and King David where not only has Jesus come, but He has sent the Holy Spirit and so the fundamental nature of our hearts has changed. We have been given the Holy Spirit who renews our hearts, convicts us of sin, and leads us in the way of Christ. But we don't follow perfectly. Even with the Spirit's influence, our hearts are still fickle.
But we have hope. Not because we can master our hearts and conquer our fickleness. We have hope because God's heart isn't fickle. He will never let us go to chase after something or someone else; He will never 'move on' to bigger or better things. His love for us is sure and constant. HE is our hope.