Without religion, also there is a way, it could be this way, through education, through scientific findings, then you get conviction. Not necessarily really love other, but for their own interest they are showing love, compassion to other like that.
When the only bond between close friends is attachment, then even a minor issue may cause one's projections to change. As soon as our projections change, the attachment disappears, because that attachment was based solely on projection and expectation. It is possible to have compassion without attachment, and similarly, to have anger without hatred.
In harmony with the Tao, the sky is clear and spacious, the earth is solid and full, all creature flourish together, content with the way they are, endlessly repeating themselves, endlessly renewed. When man interferes with the Tao, the sky becomes filthy, the earth becomes depleted, the equilibrium crumbles, creatures become extinct. The Master views the parts with compassion, because he understands the whole. His constant practice is humility. He doesn't glitter like a jewel but lets himself be shaped by the Tao, as rugged and common as stone.
Every religion emphasizes human improvement, love, respect for others, sharing other people's suffering. On these lines every religion had more or less the same viewpoint and the same goal.
Look upon him who shows you your faults as a revealer of treasure: seek his company who checks and chides you, the sage who is wise in reproof: it fares well and not ill with him who seeks such company.
A man of good sense but of little faith, whose compassion seemed to lead him to church as often as he went there, said to me; 'that he liked to have concerts, and fairs, and churches, and other public amusements go on.
If indeed the qualities such as love, patience, tolerance, and forgiveness are what happiness consists in, and if it is also true that compassion, defined as concern for others, is both the source and the fruit of these qualities, then the more we are compassionate, the more we provide for our own happiness.