How do you feel about open relationships and can they be healthy?

I've been with the same girl for 6 years and I love her to death but I find myself lusting after other girls. I would never do anything but I wonder what would happen if I ask her and see what she thinks. I'd obviously let her do what she wanted if she wanted to be with other guys. I know I'd be jealous but I don't think it would affect me if I was getting variety too.

Anyone give me some insight if you found yourself here?