As the teacher you have many opportunities to teach your students about what it takes to BE a good friend (to oneself and to others). The obvious ways are sharing stories with your students that lend themselves to discussions about friendship... choices the characters make that reflect "real" friend behavior vs. those choices that reflect behavior that is a)respectful b)unkind c) rude d) all of the above.  You can also create projects that require small groups working together... cooperation is often one of the seeds that can blossom into friendship.

Book 2 of my award-winning Middle School Confidential series is called Real Friends vs. The Other Kind. It's also about to be released as an app for 5th-8th graders.

One other suggestion... talk to your colleagues about a Mix It UP At Lunch Day (these can be done on a regular basis, as in once a week). The idea is simple, break down the walls by challenging students (typical and atypical) to sit with and get to know someone they don't already know. Teaching Tolerance has resources for teachers about Mix It UP At Lunch Day http://www.tolerance.org/mix-it-up/get-started

Expand your concept of what you're teaching your students. Friendship skills is a big part of your curriculum. You're the leader. Go for it!