There was a lot of drama that caused their divorce. I met him two years into their separation and two weeks before their official divorce papers being signed.
I always suspected she still had feelings for him. The three of us went through quite a bit of our own drama when I was pregnant with me and DH's son. TM (the mom) and I became friends eventually, but there was always some tension. Now I know why.
They've come a long way in a week and I"m truly happy for them.
It's shown my DH too that maybe a FWB isn't what he's looking for, or what he should require of me. Real feelings can be involved here and everyone still feel loved and appreciated.
Thanks for the input. Like I said, everyone situation is different and of course you have to come up with your own "normal", but I also really want poly to work for us and I'd hate to fall into some typical traps that are a bad idea is all.