Love certainly is, wishing others well and taking away their suffering certainly is. Mercy yes. But suffering with the other? Enduring someone else’s pain? Walking the extra mile? Turning the other cheek? That I think, is a totally Christian novelty.
You may want to give a concrete example of what you mean by “suffering with the other”, “enduring someone else’s pain”, “walking the extra mile”, since they can mean many things to many different people.
However, “turning the other cheek” is pretty clear. And a good example of that can be found in the Buddhist Suttas, in which a Buddhist monk is about to go spread the Dhamma (the Teachings of the Buddha) into a region of the world (somewhere in India, perhaps, or a neighboring land) that could be very dangerous to Buddhist missionaries. The Buddhist monk,
named Punna, addresses the Buddha, as Buddhists do, as “Lord” here:
“Lord, there is a country called Sunaparanta. I am going to live there.”
“Punna, the Sunaparanta people are fierce. They are rough. If they insult and ridicule you, what will you think?”
“If they insult and ridicule me, I will think, ‘These Sunaparanta people are civilized, very civilized, in that they don’t hit me with their hands.’ That is what I will think, O Blessed One. That is what I will think, O One Well-gone.”
“But if they hit you with their hands, what will you think?”
“…I will think, ‘These Sunaparanta people are civilized, very civilized, in that they don’t hit me with a clod.’…”
“But if they hit you with a clod…?”
“…I will think, ‘These Sunaparanta people are civilized, very civilized, in that they don’t hit me with a stick.’…”
“But if they hit you with a stick…?”
“…I will think, ‘These Sunaparanta people are civilized, very civilized, in that they don’t hit me with a knife.’…”
“But if they hit you with a knife…?”
“…I will think, ‘These Sunaparanta people are civilized, very civilized, in that they don’t take my life with a sharp knife.’…”
“But if they take your life with a sharp knife…?”
“If they take my life with a sharp knife, I will think, ‘There are disciples of the Blessed One who…have sought for an assassin [that is, they mistakenly actively sought to become martyrs for Buddhism], but here I have met my assassin without searching for him.’ That is what I will think, O Blessed One. That is what I will think, O One Well-gone.”
“Good, Punna, very good. Possessing such calm and self-control you are fit to dwell among the Sunaparantans. Now it is time to do as you see fit.”