Lol. Just how much do you have to hate yourself to agree to this as a guy? If my GF were to even make such a suggestion, our relationship would be over. I mean, this is probably the single biggest sign of disrespect there could ever be.
There is also no way this could ever work out. Even if the guy 'agrees' (in reality he's probably too much of a wuss to go through life single again), it can only lead to sexual frustration, jealousy or all sorts of toxic feelings and behaviour. And if you have that much of an open relationship that you don't even care about cheating on each other, why bother having the relationship at all? At the very least I wouldn't call it a marriage (the way we see a marriage today).
Oh, and as for you, don't mix with the crazies, dude. Nothing good comes of it.