My XW and I reached a civil point at about that same timeline. I can't say we have ever become "friends" since the D, but we definitely have each other's back during difficult times to ensure that our son is taken care of.
Maybe you're at a point of detachment that allows you to not care that she's dating. That's not so different from what the rest of us are trying to do with our current sitch's - reach a level of unconditional love that yet doesn't leave our own needs neglected.
