So you told her the two of you were going to have an open relationship. She somewhat reluctantly agreed, you had sex with three other women, and now she's found someone else and would like you to be the secondary. It was okay for someone else to be in the wings waiting for her when she wasn't busy with you, but you don't want to be the one waiting to see if she has time?
Just checking to see if I have this straight. Because right now, it seems to me if you thought it was good enough for him, then it certainly ought to be good enough for you, too.