My sponsors always had a best-before date, and they were never my "friend" either. I was totally serious about those steps being completed so I could get on with living my life free from my alcoholism. Three months of intensive step work, rehab work, group therapy, and the end of my being a sponsee -- and I'm still sober living a great life. Sponsors are an example until they aren't, imo. Even when I sponsored others, I had time limits and it was rare for me to agree to give more time. I never sponsored anybody more then a year.
Friendships stand best when its mutual and equal, and earned. Sponsorship is an altogether different kind of thing, and I know many people think of their sponsor being their friend, and that's fine, just not how I did it. I worked my sponsors over like they asked for it, and I didn't want friendship clouding any issues for either of us.