Salaam,
There is nothing wrong with developing a personal friendship with a non-Muslim to help him/her understand and appreciate Islam and to ultimately embrace it if they chose to.
5:5
This day are good things made lawful for you. The food of those who have received the Scripture is lawful for you, and your food is lawful for them. And so are the virtuous women of the believers and the virtuous women of those who received the Scripture before you when ye give them their marriage portions and live with them in honour, not in fornication, nor taking them as secret concubines. Whoso denieth the faith, his work is vain and he will be among the losers in the Hereafter.
from
Haqeeqat.orgToday for you all people the nutrient, nourishing things "tayyi'baate" have been made permissible/lawful;
and the [tayyub] prandial of those whom Book was given earlier also are permissible for you people, the believers, and your prandial is permissible for them;
and are permissible for you [for Nikah] the women enjoying protection of their families from amongst the believing ones;
and the women enjoying protection of their families from amongst the people whom Book was given in times before it was given to you.
And whoever refuses to accept [these restraints/injunction]/apostatizes then indeed his act has gone fruitless/wasted/weightless,
[Same information in same words in 3:85]
and that person shall be amongst the losers in the Hereafter. [5:05]