Hopefully, time will become your ally. IF the marriage with RB is truly dead, then it looks like it's up to you to build a new one with him.
If you're hurt by him being with the OBS, let him know (if you haven't). That may be part of what he's looking for. I can understand the idea that it's not purely revenge, that RB may be seeking comfort that is no longer available (in his mind) from you, or that you changed the rules of the marriage, and now he's just following the new rules (and even being more open about it). That being said, I have to think on some level he's trying to strike back, at least a little. Be as available as you can be for him. One thing is to do what you're already doing, changing the rules again. This time you will be faithful and trustworthy, and hopefully he'll eventually follow, but you may have to settle for his current arrangement for a while, and I understand applaud your tenacity - I hope it bears positive results).
I don't know what to advise really. Like always, take note of little successes, make the most of any time periods where you end up together.
You may feel you have a million reasons to say you're sorry (and are trying a million times to say it), but be aware that's no surprise to him now, and (in his mind) may be almost meaningless. There are a few other phrases which may be more effective for now, but they must be timed correctly, and they MUST be sincere:
"Thank you for that"
"I didn't expect that and it means more right now than you can imagine."
"You don't know how much that meant (means) to me after everything. I don't deserve it and I really appreciate it."
"You look (sound, smell, feel) great!!"
"That meant everything!"
etc.
Don't use them unless you can really mean them - It's sincere appreciation for moments you didn't always appreciate in the past . . . not flattery.
Whenever you must say 'I'm sorry' again, perhaps try and add extra reason (and maybe your own creative turn) to it - Examples:
"You're right . . . How could I have thrown away such precious gems for meaningless plastic baubles . . . "
"This was great, how wish I'd valued (or never taken for granted) . . ."
"I'd do anything for just 5 minutes of what I once had . . ."
etc.
There are others with advice and books that I've no doubt can be a lot more helpful in this arena.
Try hard to find things, even little ones, that you can do together. Cook, watch a show or sporting event, clean, whatever. Little steps. Hang in there!!
[This message edited by c24j at 7:23 PM, March 7th (Monday)]