Regarding Belle & Zelena,
By now it’s rather pointless to try to explain anyone’s behavior on OUAT, I suppose. Everyone has killed another character’s loved one, and if Emma’s non-reaction to finding out her fiance offed her grandfather is any indication, it’s apparently not a big deal anymore.
But for Rumbelle fans, I know it’s always a sour note that the show portrays Zelena and Belle as becoming so chummy. The former, of course, who is responsible for Rumple’s son dying. This development can be chalked up to the old standard of bad writing, probably combined with their habit of trying to showcase Belle as a forgiving character. (e.g. similar attitudes towards Regina & Hook)
God knows the show isn’t gonna try to explain anything beyond that, but if you’re looking for another reason to explain why she is acting in this fashion, may I offer this theory: