Mike, she's not a "new" Amanda, just one that has felt comfortable enough to open up some of deepest, until recently hidden away, desires. She still loves you just the same.
There is always the possibility that you will both form deep emotional attachments with future lovers, but that does not mean that things will change between you. Loving another doesn't mean there is less love to go around. It doesn't work like that. If you guys have a strong bond between you that won't change.
Be careful with making rules. Or if you feel you need them go in with an open mind that rules can be modified in the future as love doesn't always know how to follow a set of guidelines.
I'm happy to see that you are both communicating your desires to each other. Keeping those lines of communication is important to a successful relationship no matter what the situation.