Why ask without asking? Why not try the direct approach???
First, insure that there is:
Then:
and say something like, "Baby, you seem...
Then continue with, "Honey, what makes you...
Maybe you two will be able to have a good talk about this, maybe she won't be that into discussing it. If she isn't, you really can't do much about that. I doubt pushing would help, and pushing may be part of the problem.
You say, swinging aside, things are good between you two right now, and you could take swinging or leave it. Forgetting about any swinging is always an option. Could be that for whatever reason, it just may not be the right time for her right now. Just tell her you want to stop swinging because things are not feeling fair to you and that she is all you really need anyway.