Wow, you sound very calm about this, so congratulations on being so accepting of your partner's desires!
Sounds like you are doing well. Keep the lines of communication open with your hubby. It's so important!
It's also great that you would like to know the other woman better. Sometimes it's more reassuring to talk to the other person, rather than getting second-hand info.
As for not wanting any other relationships in your life, that is just fine! We are who we are. If you are happy to let hubby explore this interest and have time to yourself/with the kids/with your friends, then great!
The "right way" is what feels right to all parties involved.