Thank you all for your posts, and I'm so sorry it's taken nearly a week to get back to you. DS has been poorly, and I have been on the phone lots with DB (including in the middle of the night again) and thereby messed my sleep up this past week.
Well, I'm relieved that I'm not being an utter bitch for needing some boundaries here. I thought the "compassion fatigue" term hit the nail on the head.
Ah, Miggsie, I can relate to you. I think you have better staying power and tongue-biting ability than me! It sounds like your brother is caught in a bit of a codependence trap, which is tough-going for all concerned - sorry to hear this.
Ronaldinhio, you are absolutely right: it does take two to tango. My opening post describes where DB's "relationship" is at at the moment, although I know, he knows, we all know that he behaved out of order towards the end of last year, and that this was the straw that broke the camel's back. He wasn't unfaithful, and he didn't hit her, but he shoved her once. No marks or pain; just downright disrespectful. They were having a tense time due to other stuff going on in their lives, and I understand how tempers could have become frayed, but would emphasise that it absolutely wasn't OK of him to do this.
What I get angry about is that DB has spent the best part of a year taking all the blame for the marriage going tits up - he seems to willingly take the blame, and she piles it on him further. The fact is, he did something wrong at the end of an already tense year. He has apologised repeatedly. He has sought help to manage his temper. He has done everything he can do to mend his ways bar erase history. What winds me up no end is that where his wife should either forgive him and they move on together, or state that DB's behaviour was a dealbreaker and leave, she's conducted an affair for the best part of a year, telling DB he "deserves" this, and it's still going on, and she doesn't intend to stop yet "because it'll make me depressed" but she has told him to stay right where he is. And the silly bugger is doing just that!
In my mind, when a relationship has gone off the rails as theirs did a year ago, the couple get into counselling and thrash it out - or move on independently of each other. But it can't be dragged up and dragged on endlessly, with blame being apportioned and guilt felt left, right and centre, and affairs continued as some kind of punishment, ad bloody infinitum.
DB's done and is doing all he can. She won't budge - won't quit the affair and won't see a counsellor. I bloody wish he'd leave.
As you can tell, I get sooo angry about all this! Suffice to say, DB and I have had some good chats this past week, and I have said to him that I can't keep listening and feeling the pain of what he's going through with no end in sight, which he understands. I've asked for a breather, and he's respecting this.
Thanks, all, for helping me feel like less of a bitch for bailing out with the listening.