Peter goes back inside to apologise to Eric for snapping, but it's unclear from Eric's reaction whether he really didn't think much of it or just didn't actually remember the details of what had happened beyond "Peter looked upset and was snappish because of it". He then interrogates Eric a bit about this "past life" business and finds that Eric was actually Alexei's sibling in his past life but also he didn't remember what exactly his relationship with Zachary had been. 

And they never thought to share details with each other to put it all together. Of course.

He doesn't get Alexei's own perspective on it, though, as the man leaves reasonably soon after that due to being too overwhelmed by the crowd. The way he does that by summoning an enormous scythe out of thin air in a puff of black smoke and a funeral bang of a disembodied cello and organ keys does make the account that he is in fact the Grim Reaper reasonably likely but who knows, really.

Anyway, the party keeps going for a while even absent one of the grooms because the other groom is very clearly deep in his element, there, and having a blast. Also there's the thing where everyone is weird and doesn't find it weird at all for a wedding party to keep going with only one groom but sure, whatever, Peter has fun.