Had this in mind while watching again and spotted that the calendar under their anniversary photos says February 2022 during the flashback to their I don't love you anymore argument. Wen is clear there that in his mind they are already broken up. Alan seems to accept this at the time and agrees to be friends.
Their first anniversary was in May 2017 btw, so May 2022 would have been their sixth anniversary. There's no photo for that of course.
The majority of ep 5 takes place late December 2022. Jim and Wen meet 10 Sept 2022 (on Jim's beer). So six full months (March-August + ? weeks) between flashback argument and Wen and Jim sleeping together and 10 months between the flashback and Xmas arguments. Add in however long from initial breakup to flashback argument.
I didn't realise Wen had keep it in limbo for THAT long. My dear boy, what were you thinking? (Before this, I'd assumed the flashback argument was fairly recent.)
Getting this down whilst I have the dates fresh in mind. Will be back after I watch the rest. From what I remember of Alan and Jim's conversation re timing, I think there might be some internal inconsistency between the visual date and dialogue.
Re the ring - Jim and Beam also had rings. It may have been couple's rings like in S Korea but I think it's more a sign they saw themselves as married even if they couldn't register it and get it legally recognised. Possibly somewhere in between, but it's clear the rings indicate long term commitment.