She wants more than just you !
I have been married more than once and one of them was a real hot young lady.
We had an affair when she was married to someone else and which ended up with her divorcing him to marry me.That was great and I felt really lucky until she started wanting to go out and so on.You probably get he picture right now and although she never talked about it I was obvioulsy not the only man that was sleeping with her.
If you are in love with someone an open marraige is not really a good idea as it will hurt but if you only care for them even love them it can work.That was the case with her so she went out a played a bit while I took on mistresses over the years.We were married for over 10 years until yes I fell deeply in love with one of those young ladies I had been dating.
I divorced my wife and married the mistress , so yes I am eternally happy but when you play with fire your fingers can get burnt.This is what happened to my ex wife and everyday I feel a bit bad about.The concept of multiple partners/ lovers within the bounds of a marraige is fine but remember she might fall in love and divorce you.My moral is if you are out of your depth get out and fast.