When relationships end there's usually pain involved. Pain that lingers.
Perversely this pain can flare up because of happiness expressed by the other party. Where happy signs are interpreted (real or imagined) as a kind of insult almost. "Look at me doing great without you!"
Which in itself can also be a way of coping with a situation like this. By communicating your hapiness you're trying to make it last, become a new foundation of hapiness to replace the one that was lost.
And nothing can help with something like this really, except that old adage 'time heals all wounds'.
I think both need time. Time to build/transform their lives into a world where the other is truly no longer a part that is sorely missed at some level.
I think the Mute function is an excellent suggestion. I'm sure the both of you are not intentionally seeing each other in real life, so look at it like a time out. You both go your own ways without being confronted with each other all the time. I'm sure that with time the mute function will become unnecessary. But I also believe this will take at least a year.
In the meanwhile us other forum members will not feel as being forced to choose between two forum members we've come to like and appreciate. (and the both of you won't have to weigh your words just because of how the other might interpret them)