I'm just curious - have you two figured out why the intimate physical connection isn't there anymore?

Until you figure that out, non-monogamy will not be the answer to your problem.

Unless, of course, it's due to something outside of her control (health, etc).

I think it's great that you two have come to a compromise in that way, but fair warning - sleeping with other people adds a new layer of problems (or stressors, at least) that will either hurt, or help, the current relationship you have with her.