Sounds like you two need a heart-to-heart discussion on your relationship, satisfaction, and desires for more.
It sounds like she is justifying her online-relationship to herself by convincing herself that you're outside the martial bounds as well.
Frankly, you both appear to desire a somewhat more open marriage. If you're cool with it, maybe she is too. But you need a VERY strong foundation to build from! And that starts with you two being COMPLETELY honest with one another. Because it only gets more complicated, LOL.
Good luck! And just be yourself and be honest. She loves you and married you for a reason.