So I agree people change and so marriages change. I'm of two minds on this for a major reason. DH and I were married more than 15 years, mono both of us, when we opened to poly. My main resource was a poly/mono online group that I have left.
See, I was surprised by poly. Sure we look back NOW and see signs of it from dating in high school, but we were caught unawares. So many are when they've been married for a long time. And sadly, what catches them unawares is already falling for someone else. So you don't just have a married couple suddenly confronted with poly. You have a married couple blindsided by an affair and the refusal to give up the affair. That's where the unfair part comes in.
Not only is the person who is blindsided suddenly having to understand there are other forms of non monogamy, but their partner has had an affair. This is really really hard to deal with and for rebuilding trust takes years to work out, if ever.
Personally, my problem is that there is a kind of attitude that the person who cheated is a 'poor poly'. Someone that had no idea they had options so HAD to cheat. Who is somehow the victim and society has done them a great disservice. They do not feel the need to be portrayed as a bad guy in any sense. They do not have to apologize or feel any guilt at all for breaking the trust of a relationship. They really just need to tell their partner (spouse) that poly is okay and show them articles on how to get over their jealousies and have compersion!
This annoys me to no end and is the reason I will never, ever, point someone to that stupid list. Not only are the people that cheated told not to feel guilt or try to restablish trust, they are coddles and patted and told what a victim they are. Then, when they inevitably lose their marriage, it's not their fault. When they then lose their poly relationship they refused to give up in order to repair their current relationship, it is again not their fault. There was too much coddling.
Which is why I prefer this place. Sure sometimes people seem a little harsh and you better believe there are people here who I don't agree with and so who's opinion I disregard. However, no matter how scary it is to the poly person to suddenly realize that they CAN love more than one person, no matter how upset they are at a mistake as huge as cheating is, they are not allowed to keep their victim card and be coddled. People are called out here. It may not always be appropriate or kind, but it's necessary. I tire of being told I shouldn't feel guilt for mistakes I made in my marriage when it comes to falling for someone else. If I don't feel guilt, if I'm not willing to put in the work, then how much could I possibly love my partner?
Long story short, yes, we married people can be blindsided with realizing we are poly. Just as someone can be blindsided with the truth of their sexuality. No, not everyone handles it well in a mono relationship, but not everyone is pulling one over on their spouse just to have the best of both worlds.
Me: Late 30s pansexual poly.
DH: My husband of 19 yrs and father of 3 teen girls.
DC: LDR of +4 year