You're going to have bad days and good days, and your emotions will be all over the place. This is normal. The process you're going through doesn't happen on a straight line. It scatters all over the place. Just when you think you're going to be OK, bam! you're back to hysterics again. In fact, there'll be days you have more than one emotion at the same time, and that will really make you feel like you're going crazy, but it's all completely normal.
Now I don't know your story, but you are seeking professional help, right? Getting therapy, getting anti-depressants and all that good stuff, right?
Now, here's another thing. You can't let him have you and the OW. You have to set boundaries. He sounds like he cares for you, but he's going to do what he wants to do, and you have to let him. Start by telling him to [censored] or get off the pot; either he gives up the OW or leaves the house. That will stop that misery you're going through, it might make him give up the OW, but if it doesn't, then it will throw him into her arms, and that's a good thing, because then their affair has a better chance of ending more so than if he has his cake and eats it too. Plus you'll have established boundaries and respect for yourself, and he'll have to deal with that, meaning that you'll have taken back control from him.
