

It really depends, but ultimately a lot of social interactions can only happen between two people at once. Say you and your wife get into a fight. Instead of fighting it out & making up, she now has the option to stop fighting you and go hang out with your co-husband - and you aren’t invited. She also has the option to emotionally strong arm you to get her way by not only stonewalling you/withholding affection, but also by threatening to push you out of your marriage for another guy who literally lives with you both. Conversely, she does the same thing to the other guy.
Basically, now all those 2-person social interactions that happen in a marriage become much more complicated due to the presence of a 3rd person.
You’d need to have a lot of trust in your wife (and this other guy too) - she’d need to have a tremendous amount of emotional stability and be non-manipulative. She’d suddenly have a lot more power in the relationship in a very inequitable way.
My wife and I are very into monogamy. But she has a serious temper and can be very manipulative when she’s angry (she’s gotten better about this, but it’s a known issue). It’d be very easy for her to do something hurtful. I’m not talking about sex, just the emotional threat of turning to someone else for relief from me - and the implied threat of pushing me out.
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