I dont believe you can be a supporter of 2 clubs. Surely being a true fan is about putting your club & its colours above all others?
Just because you enjoy Arsenal's football, doesn't follow that you support them, it means you like football.
While you can't truly support more than one club, we can appreciate good football, & want to watch it. Watching Arsenal, the Dutch NT or Manchester is to enjoy your football, seeing those teams in full flow is a thing of beauty. However, while I can stand & applaud those teams, I'd never class myself as a supporter. Take Italy's great performances in the last WC, Boz can see the beautiful football, clap & cheer with the rest of us, but come next month he's a Scot, & hopes we all choke while Faddy sticks one in top corner (not gonna happen Boz, but enjoy the dream while it lasts

). He liked our style, but that doesn't make him a supporter.