Lyric discussion by APipeDream 

Cover art for The Wolf lyrics by Mumford & Sons

I think this is about a relationship that ended, and The Wolf is the other man. The chorus alone sealed at least my interpretation of the song:

"I've been wondering for days how you felt me slip your mind" seems like the person he loves doesn't feel the same anymore. Then, "Leave behind your wanton ways", meaning drop the promiscuity. Maybe an affair? "You were all I ever longed for" describes this as a relationship in the past, which he clearly felt was going somewhere.

My Interpretation