I have had the blessing of spending all weekend with mentors and friends. Fortunately my main mentors are my parents, and my main friends are my siblings, but some how these roles are illuminated by spending time with other mentors and friends.
Sometimes mentors are distincly mentors - oh, you spend time with them and have fun, but there's obvious enough disparity of age, maturity or experience that it's a mentorship more than a friendship.
Then there's more clear friendship, usually with something like a peer (I wish I had a better word than peer, which bugs me, but I'm working on it.) That said, I believe the best, truest and most lasting friendships are something like mutual mentorships, where both friends have something to offer and something to learn, and in turn call one another to a higher level of holiness.