Get Haven and Life Rip for sustain, and take Rogue's Gambit for mobility or Artful Dodger for even more sustain. Also keep in mind Lex's Retribution; always be prepared for an ambush.
Just remember that Lex has to be close to you in order to maximize his damage output, so poke from long - mid in order to have the best chance against him, because your daggers don't have a damage fall off (´・ω・`)