T0 nailed it. Your job when H is home is to act like in the week you didn't speak to him, you had an epiphany. You realized that this may not be what you want, but you're going to be fine. Actually, you're going to be better than fine. You're going to be HAPPY.
Since it seems, according to the information you have provided, you have been really weak and clingy in front of H since BD, it's very important for you to remember these things:
1. You can't talk sense into him. Don't even try. Don't mention the separation. Don't mention the OW. Don't mention your relationship with him. Don't mention your changes. And don't repeat your wish to save your M. Don't repeat that you're going to "stand" or fight for your M. You've already said it once. He knows. If you repeat it, you look like a weak doormat. Don't go there. You're not a weak doormat. If he tells the kids about the A, fine. Your kids are grown, yes? If your kids ask you questions, be honest with them. Don't make digs against your H. But don't lie to them if they ask you questions.
2. Have plans to go out, but don't tell H about your plans. Dress like a million dollars. Wear a new perfume. New jewelry. Be mysterious. Don't be mean. Don't be short and snarky. Be light and breezy. Yes, you're going to feel like you're dying on the inside. No, your new attitude will not drive him away ... as long as you're not being sappy or b!tchy in the meantime. In fact, your new attitude is going to make him a little curious. He may ask you where you're going. Smile and say, "Out with friends," then keep on moving. He may ask you what time you'll be getting home. In passing, say in an upbeat way: "Not sure! Probably late. Make yourself at home. Don't wait up!" Will this make him feel like you're moving on without him? Yep. It will. And despite how you're feeling right now, that's EXACTLY what he needs to see. Because the truth is: No matter what he decides, you WILL be okay. I'm not asking you to be cheerful and happy to mask your feelings of hurt and pain and rejection. I promise I'm not. I know those feelings are real, and there's a time and a place for you to deal with them, alone and with safe, trusted friends. Your H isn't safe right now, and you can't trust him. He has fired you as his W, and he thinks he's already found your replacement. He is disrespecting you - and your M - to your face. What I AM asking you to do is to believe in you. I'm asking you to try to have a positive attitude while his eyes are on you. I'm asking you to do something that makes you feel good about yourself - strong and powerful and confident, just like you were before you met him. (THOSE are the attributes that made him fall in love with you in the first place, right? Would he have fallen in love with you if you were clingy and weak and needy and sappy? Of course not!) I'm asking you not to fall to pieces in front of him - in anger OR in pain. Don't let him see you sweat. Don't give him that power. If you need to fall apart, do it when he isn't around. You've earned it. Cry your heart out. But not in front of him. More than anything, I'm asking you to gift yourself some dignity in the face of your long-time H having an unrepentant A in your face. This is to make YOU feel better. It has nothing to do with him. You walk around that house like you are the ruler of the roost. Because, sweetheart, you ARE. Don't let him allow you to forget that. There may be a time for you to listen to your H and to validate his feelings. Right now - while he's in the middle of an A - is NOT the time.
3. DO NOT have sex with him. This is in consideration of your health and life. He may try to initiate it just to see if he still has you where he wants you: Plan B. Don't give him that. As Starsky says, people - and most definitely men - want most that which is difficult to obtain. You're not easy. Leave "easy" to the OW. Your his W, and, yes, you should be able to ML to your H. But he's not your H right now. He's someone else's sexual play toy. I know that hurts to hear. But you should rest assured that that's usually ALL affair partners are: ego boosters and sex toys. And they often get discarded just like broken sex toys as soon as the fun wears off. Trust this.
4.. Do whatever you wish with your rings. That's a personal choice. If I were your H, I'd find it odd - and, frankly, a little pathetic - that you started wearing your marriage-related jewelry AFTER I had left you in part to spend time with OW. I understand the ring only fits now - congratulations on your weight loss; I love hearing when people here are able to do it in a healthy way like GAL and bike riding ... I lost 20 pounds from not being able to eat when my H left (unhealthy as heck, but I couldn't stomach food) - but the locket? Why would you wear something so sentimental, that represents your M, while your H is choosing to spend nights with a woman who is working right alongside him to try to destroy your M?
It's time to get a little angry about your sitch, sweetie. It's time to take your power back. It's time to take your dignity back. Don't let him chip away at those things for one more second.
He's only going to be home for a limited time for this visit. Make it count. Give him something to think about. I bet OW will be the one wringing her hands and pacing the floors, wondering what he's doing with YOU while he's at home. Be the better woman. (You ARE the better woman, so BE HER.) At the end of his time here, make sure you've left an impression on him so that when he looks at OW again, he thinks: Geez. I think I've been backing the wrong horse lately. You and I KNOW he has. Time to show him.
M: 40 H: 44 Married 14 years S11 & D6; D20 & D19 from previous M 2BDs/PAs, 8 years apart Piecing: April 2014