One more quick thought. It's hard to tell from out here because we don't have the benefit of all the verbal and non-verbal communication you've had with H....but is it possible that the biggest thing holding H back is that he doesn't look forward to the process of ending "it" with OW? Has H had trouble steeling himself to have difficult conversations in the past? Having that convo with OW will probably make him feel like a real jerk, especially since she is disabled and her S has probably come to see him as a father figure. It's hard for anyone to have someone "hate" us and I'm guessing your H is having difficulty preparing himself for this.
