I don't know about mutaa, but I know in misyar, the same thing above applies. There are a lot of women in America who don't know their husbands have had multiple misyar wives that they take when traveling and stuff like that. If I was married to a daiyee, shaykh or pop nasheed singer, I would have serious doubts about my husband's fidelity.
From personal experience (mutah) I know that you don't need to tell your temporary wife that you are getting another temporary wife. I know this because I was looking for a way to cheat on a girl I was seeing. And there was!! And this is what happens when you give humans (in the case as in most cases with Islam, men) free reins to do as they please without feeling guilty, neither over their faith, with god or with their wife.
But if she sees somebody else while you are with her, you need to do the whole temporary marriage thing again.
Incidentally, I had the intention of cheating with this girl (in mutah), we weren?t really together, I never did cheat though (not because I didn?t want to, it just fell through). She even asked me if I had been with another girl, and I said no. Months later I found out she had cheated on me, again cheating is a harsh word since we hadn?t fully agreed on the specifics of our relationship, exclusivity to each other being the key term though and with that I would say she did in fact cheat on me. She also had the intention of cheating at a separate time but the guy fell asleep lol I heard all of this from the guy himself, we?re friends.
I didn?t feel bad or angry or anything when I heard, her opinion was that we were more friends with benefits but still felt cheated (later on during the relationship I felt she was more of a gf).
Any case, important lesson learned, don?t fucking cheat, it hurts (even at this level where we weren?t fully together). I know it sounds like I?m apologizing, and I am, its shameful I know, it?s also shameful that this is a religion for all of mankind for all of eternity, and can be perpetrated on our mothers, sisters, wives, daughters, cousins, nieces, aunties, grandmothers, basically all women dear to us. I know that if this happened to my mom I would be sickned and hurt, and if action can be excused according to this religion (which seems likely) then it?s not a fair religion, not a just one, not a fair god, not a just one, and obviously a religion founded by men, for men.
You know.. it would have been so much more ethically honest, if we had said we are friends with benefits, end of story, we can see others, or friends with benefits but exclusive (which is what we agreed upon, but she cheated, and I had the intention of cheating) or saying no we are a couple, we don?t see others. Basically you choose how you want the relationship to be, and if somebody fucks up then it?s on them, they are in the wrong, and its up to you whether to forgive or not.
EDIT
OK re-reading my post I come across as I don't know somebody in denial, point in case, she did cheat on me, i feel bad about saying it because i had the intention of cheating, so how does that make me better? And the second point, my friend, he didn't know i was seeing her, we weren't even friends when it happened, and he asked me if i was angry and i said no. god this is like a therapy session
Topic: Does a muslim husband need to tell his 1st wife that he's getting a 2nd wife?