I know Fuck Facebook but did you know Facebook has so many copies in Russian, Chinese & in many languages you don't even know exist. But no one ever catched up to Facebook because it adapted. So don't be a baby when someone copies you, be flattered. Let them copy, make sure they don't catch up with you. If they offer something better than you then obviously people will choose their product. Competition brings the best out of you. If Gumroad would have did it right then SendOwl or Paddle wouldn't have existed. But they are the same ideas. As Adil said its inevitable.