Is it wrong to be in a friends with benefits relationship with an ex?

[Sur La Mer]

Leave the EX's behind, they're YESTERDAY.

Looking back, only brings more drama, move forward to tomorrow!

Done that, was curious what it was like, and ended up gradually, but there were closures, FINALLY a happy death.

My son does that, all the spouses hang out together! I saw the ex @ my son's last week, without her husband/bf, and my DIL are friends with her too. But the ex is not as happy as she is on Facebook, when all the girls are together, but I'd like to know her husband/bf because when I saw her, she looked lonely and pathetic hanging out with my son & his wife. In order for me to judge, I'm waiting how it all ends up. It's healthy for them, but for me to judge, I don't think it's healthy.