Should we have only Christian friends? No!
We should be a great friend to everyone. We ought to love the people around us and be helpful to them and build good and healthy relationships with them.
Use the opportunities that we get to be kind to them.
Good friendships are the ones where we can trust each other and help each other grow.
It is also good to have friends who are Christians as it'll help you to grow spiritually and pray for each other. But limiting our friends to just friends who share the same beliefs and rejecting others is not a great practise.