When you lead, friendship should not be the number 1 priority ; as inevitably there will be extended  tolerance for non performance and that will be detrimental for him/her, yourself and the company too.

Continue to demand the best from your subordinates. Be strict, be demanding and if friendship can grow,  that is great.

As a leader, your primary task is to focus on  performance and to grow others : & not being a “nice buddy” to everyone