Introduction to the Devout Life by St. Francis de Sales (Church Doctor)

This book has a few specific chapters on friendship that are very very valuable.

Download this handy PDF for A4 paper:

• http://sites.google.com/site/catholiclifetimereadingplan/file-cabinet/intro_devout_life_brief.pdf (emphasis on the practice of virtues and friendship)
  

• Full version at a respectable website: http://www.catholictreasury.info/books/devout_life/