I think pity should be given to Ella since she tried to do good (and was beloved) before and after she became a nun.
......and whatever it was that Ella discovered once inside her wedding ring was probably not revealed to her prior to it being placed on her finger. I think, whatever his sexual preferences, Serge was a difficult man, whose moods could not be second guessed. My understanding is that Ella handled the situation calmly and serenely, and stood steadfastly by her marriage vows, putting her energies into doing good, rather than seeking hedonistic pursuits.