So, I may not be the right person to comment on this because I was the "new wife," and also I don't know what Americans consider acceptable to discuss, so forgive me. But... if I'd been my Husband's first wife I'd have honestly been relieved to hear "dorogaya, I'm taking a second woman." My Husband has... let's say a "ravenous appetite for the pleasure only a woman can give," and I think I'd be intimidated, and more than a little bit exhausted, if I had to keep my Husband happy all by myself.
It's also nice to be able to say "honey, I need some time to myself" without feeling like I'm shooting him down. When you're monogamous, if he is lonely and you need space, you have to put aside your own needs and please your Husband. With another wife, I can say the same thing and my Husband smiles, kisses me once and goes to spend time with one of my sister wives.