[good times]

I know very little about Poly style relationships but it sounds to me from what you have related here that what you want with her is a poly relationship and what she wants is more of a traditional open swinging relationship with you.

I also agree with what Spoo said and think she may avoid telling you before hand because she doesn't feel the need or desire to have a confrontation with you about something that she probably feels isn't your business.

I think you are doing the right thing in backing off from it because it is pretty apparent that you both are not on the same page regarding your commitment to each other and what the bounds of your relationship should be.