Good heavens, Man!!
Sounds like your wife has brought up some topics that some men around here would love to have their wives bring up! Go for it!!
Seriously, if the communication between ya'll is such that she has felt comfortable mentioning being with a woman, and she has related to you comments made by this friend that might be suggestive, I would simply talk to her about it. Seems that she has given you the opening you need. This may just be her way of trying to see if you might be interested. No harm in talking to her about it.
Let us know the outcome.
EBF