REASONs FOR BEING UNFRIENDLY WITH DISBELIEVERS:
Allah has forbidden the Muslims from being friendly with enemies of Allah and His Prophet.
It happened when the Quraish broke the treaty of Hudaibiyah, the Prophet (peace be upon him) started making preparations for an invasion of Makkah, but he did not tell anyone, except a few close companions. At about the same time a woman arrived from Makkah,
Who had been a slave-girl of the Bani Abdul Muttalib?
She complained of poverty to the Prophet (peace be upon him) and requested financial help. The Prophet (peace be upon him) appealed to Bani Abdul Muttalib and he satisfied her need. When she was about to leave for Makkah, Hatib bin Abi Baltaa met her and quietly gave her a letter addressed to some of the Makkah chiefs and paid her ten dinars so that she kept secret and carried the letter to the addressees secretly. When she had just left Al-Madinah, Allah informed the Prophet (peace be upon him) of it.
The Prophet (peace be upon him) immediately sent Ali, Zubair, and Miqdad bin Aswad after her. They demanded the letter from her and they brought it to the Prophet (peace be upon him). The letter contained information to the Quraish that the Prophet (peace be upon him) was making preparations to attack them.
Abdul Muttalib had been treacherous to Allah and His Messenger and the Muslims. This man had participated in the Battle of Badr hence forgiven. So Allah says not to be befriended since they are Allah’s and your own enemies.
Disbelievers drive you and Allah’s Messenger (PBUH) out of your homelands. They are against your beliefs and confront you regarding your greatest glory, i.e. belief in God Almighty as your gravest sin and crime as a consequence of which you have been driven out of your homeland by them. Thus, it would not be befitting had you expressed your affection toward them.