Any talk of what you can or can't do aside, I think it's quite reasonable to have an issue with this. My personal feeling is that, if I LOVE someone, heck, even if they're a friend that I just LIKE, and someone treats them like crap, I'd have a problem seeing my friend or loved one treated like crap. I wouldn't want to be with someone who treated my friends badly.
If this is what's gone on in the past, there's no reason to think the trying to break up your marriage will stop now. If they've both been willing to lie to you in the past, do you have reason they're going to be 100% honest with you now?
Women are absolute Mistresses of manipulation.
I am upfront. I don't manipulate or play games. My female friends are the same way.