Delnaor had loved Elora but once and that was enough to sentence her to death. He could not be there for her when she needed him the most and now was left to grieve her parting.
Elves and mortals just don't seem to ever get a chance at happiness. This is one set of Mira's grandparents. Delnaor being a high elf, allowed for Mira to be raised amongst the elves.