I've had a facebook account for several years but my overall sentiment toward it has become rather guarded. A young lady with whom I was friends in elementary s

I've had a facebook account for several years but my overall sentiment toward it has become rather guarded. A young lady with whom I was friends in elementary sent me am unsolicited friend request. She was someone I'd been quite content to never hear from again. So I put my settings as private as I can and remove my profile from google. Then about a month ago, facebook suggests a friend who shares no mutual friends with me, whom I've never mentioned, and who I hadn't even seen in years. How did facebook know I knew this person? So now, I view facebook as a Rolodex. If I need to contact someone, I'll go there, but that's it.