Welcome to our forum.
I think you're doing the best you can in an awkward situation; you didn't want to lie, but you agreed to not be the one who brought up the subject.
It's really up to you whether you stick with this boyfriend; I guess it largely depends on whether you can tolerate his dishonesty. If he could lie to her, you don't know whether he could lie to you also, so I guess that's something to think about.
Try our Dating & Friendships subforum
if you haven't already been there, it might be a starting point for finding people in your area. You could also try googling "New Orleans polyamory" and see what turns up.
I hope some of this helps.