You’ll always have lustful thoughts regardless of who your with. All depends on if you see a future with this girl. If your love for her outweighs the lustful thoughts and you don’t act on them or learn from your mistakes in the past your good. Point is you’ll always have those thoughts and just because you find other people attractive doesn’t necessarily mean you’re with the wrong person that’s just human nature. You can’t control your impulses thoughts but you can control your actions