All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
It is not permissible for a Muslim to give allegiance to a disbeliever, love him or befriend him, whether he is Jewish, Christian or anything else. Allaah The Almighty Says (what means):
There are many verses that support this fact. In a narration on the authority of Abu Moosaa Al-'Ash‘ari once ‘Umar ibn Al-Khattaab reproached him when he appointed a Christian scribe. He asked him how he could maintain close ties with them when Allaah The Almighty has distanced them. He further asked him how he could honor them when Allaah The Almighty has humiliated them. [Ahmad]
However, this is different from kindness, meaning doing good for peaceful disbelievers and being just to them. These are things that Allaah The Almighty approves of. That is because kindness, justice and not being oppressive do not require one's love, friendship or brotherhood.
Allaah The Almighty Says (what means): {Allaah does not forbid you from those who do not fight you because of religion and do not expel you from your homes -- from being righteous toward them and acting justly toward them. Indeed, Allaah loves those who act justly.} [Quran 60:8]
Thus, it is not wrong to be kind to or act justly with a disbeliever as long as he fits such a description [of not fighting or expelling Muslims].
Allaah Knows best.