Did this change by now?
I talked to Friar, and he told me it was hidden.
The only thing I can do with Boris is Threaten/Kill him or give him some pleasure.
Went to the Tree with vampiric vision in a save before talking with Boris, but there is no ring anywhere.
Viewing post in Bypass Seduction in Heirloom\Wedding Ring Quest
The ring is by the same tree Kalyskah would have sex with Boris. But it only appears after you talk to Friar being gentle and then talking to Boris and being polite but not going through the path that they have sex. I can't remember on top of my head the exact choices you need to select, but I know talking to Friar is a key thing because he will tell Kalyskah that the ring is burried.
Oh yea, thanks for the reminder "Bugged" is a good word. When fighting the 'evil brother' (forgot his same) I managed to get stuck everytime after the cutscene were we rip through him. I think I could move again if I saved at that point and reloaded that save again. One time I could see the body of him still standing but inside me, which probably caused that bug.
I guess it would work if you'd move his body a bit away, so we're standing next to him, not over him.