I think if you want to continue to swing, you should acquiesce i.e suck it up.
If you're really not worried about losing her and she enjoys the meetings then if I were you I would work on my own attitude. Marriage is compromise and you don't always get what you want. I think that most guys would agree with me when I say that in this lifestyle you really have to keep the women happy. I'm not saying you're not entitled to your feelings, its just that she is entitled to her feelings too. And...If you give yourself a chance you might find that you can take enjoyment by seeing her enjoy herself. In our own experience some of the hottest/most fun sex we ever have is when she returns from a solo date with a guy or couple.