What opening do I learn?

@1
"I am 1000 Elo" ++ Then do not worry about openings.
You do not win or lose because of the opening, buty because of tactical mistakes.
"I don't know what opening to study" ++ Study none, just play and analyse your lost games.
"I don't want openings that I use only for my level and then when I improve I just throw it away" ++ Then stay away from gambits, except Queen's Gambit.
"an opening that would last, and that would confuse my opponents"
++ Openings that last do not confuse. Openings that confuse do not last.
"that I would have an advantage in the middle game or endgame"
++ No opening gives you any advantage. Chess is a draw.
You get an advantage after your opponent makes a mistake.
Simplest and best for beginners and World Championship candidates alike is
to defend 1 e4 e5 and 1 d4 d5 as black and to open 1 e4 as white.