What comes through, to me, is that your H has the desire to be with you and want to be a family, but does not have the ability to get out from under the OW influences. That could be for so many reasons, he doesn't want to hurt her feelings, he cares for her, or he is just totally clueless to the ramifications it has on your M. Sure he hears what you say, but it isn't hitting him on some type of level that needs be to take action.
How should you proceed? I think the beginners mind is a good idea. Start looking at this from a whole different perspective. Reread that chapter, see if it gives you any new insights. This has been an issue for so long for you, that I'm sure you have been thinking of it in one way--the resentment that came boiling over when you spoke to SIL, but are there other ways you can look at it and define new actions to go with that thinking?
