I understand not wanting arsenal to win. Who wants to see their local rivals be more successful and win things?
If we were in the same boat with forest then the best team deserves the league. All you can do is focus on your goals and aim for the highest place. Given that champions league was still a possibility, you've got to win and fight for it until you are out (or in). Give it a go next season and hope for the best outcome.
Forget rivalry, accept it like a man/woman and move on.
Winning mentality should be there every game.