You are doing absolutely fabulous-well done-this is a hard thankless job and especially when your friends and family think your delusional and should be moving on-I have stopped talking about my sitch to most people as I couldn't bare the looks of pity and worry tbh-so come here to talk to people who have better insight into what motivates us to carry on
Your husband sounds depressed-give him space to work out that it's not you or the marriage-if your DB and being consistent with 180's - once the pressure of any R talks is out of the way -he will start to see through the fog-it takes time and patience- act as if u are happy no matter what happens.
You are a incredibly strong woman!
As for the SIL-some people are just selfish- take comfort from the fact that you are not one of these people-you are a caring understanding supportive friend- don't forget that- treat yourself now how you would treat a friend- be gentle and kind to yourself.
