Okay. How about....
"But love your enemies, and do good, and lend, expecting nothing in return; and your reward will be great, and you will be sons of the Most High; for He Himself is kind to ungrateful and evil men. Luke 6:35
I do believe showing them the Love of God is potent in repelling the effects of the world that has people's love turning cold.
Never pay back evil for evil to anyone. Respect what is right in the sight of all men. 18 If possible, so far as it depends on you, be at peace with all men. 19 Never take your own revenge, beloved, but leave room for the wrath of God, for it is written, "VENGEANCE IS MINE, I WILL REPAY," says the Lord. 20 "BUT IF YOUR ENEMY IS HUNGRY, FEED HIM, AND IF HE IS THIRSTY, GIVE HIM A DRINK; FOR IN SO DOING YOU WILL HEAP BURNING COALS ON HIS HEAD." 21 Do not be overcome by evil, but overcome evil with good. Romans 12:17-21
I used the above verses from Paul in Romans because most people perceive v20 as a method that would revenge the other person's evil against them. Instead a commentary on these verses in being able to explain a method by which ultimately the change that we seek to happen by your question happens. A positive change/reversal in one who may not be seeking it or behaves in the complete opposite of who they once were. You would think that the one who has known love might be more easily convicted and open to change.
Now as far as v19 it's better to leave getting back at a person to the Lord, so our retort should be in providing the avenue by which they may be convicted for their wrongful actions. If seen in the following light. I think it very well might be the way to help change that heart. As the writer Paul explains in v21: "overcome evil with good".
"The picture of putting coals on a person's head initially sounds like a picture of causing burning pain, but it really is not. Instead, it seems to be a picture of stirring up the coals of a fire to rouse it back to life again. It is a picture of stirring within a person a response of remorse, when they see your kindness in the face of their meanness. This must also be the sense of Paul's passage - we cause our enemies to be remorseful for their actions toward us, and in doing so we overcome evil by doing good."
Still, brother. Can we reignite a heart that has known love but is now cold? Can we change a love that has "wax cold" by doing good? Maybe, hot coals is what is needed to those who are "cold". I would say it's worth a try!!!
Thanks for the post.
With the Love of Christ Jesus (Maybe this way!!!).