So sorry you're here, but you are in good company - familiar company.
What you're experiencing is 100% normal.
And yes, you are going through the infidelity diet, something most all of us go through, whether we like it or not. I lost almost 30 lbs in 1 month, and I'm a relatively thin guy as it is, so it was kind of a big deal for me.
I would strongly recommend an STD test. My WW told me she and her AP used a condom at all times. I 80% believe this. The other 20% says maybe they didn't, especially since most all their sexual encounters involved quite a bit of alcohol, and she also has amnesia about one of her first affairs back in 2006 and doesn't even remember what they did, sexually. That being said, when she told me they were always "protected", I believed her at the time, so I didn't get an STD test. Since it's been many months since he last fucked her, and both she and I have absolutely no symptoms, I don't feel the need to rush out and get a test. Though, if I had to do this all over again, I would immediately get a full STD test. I did, however, get a paternity test, because she revealed to me that she was screwing around on me both PRIOR to and AFTER our child was born.
In terms of the OW, I know you want to know everything about her and wonder WHY WHY WHY, but it won't serve any purpose. That, I can promise you. You are a MUCH better person than she will ever be. Good people don't sleep with married people. Period. She is NOT a good person, and neither is your WH. Though, your WH may get himself back on track to becoming a good person, but he'll have his work cut out for him.
The best advice I can offer is for you to read the 180 in the Healing Library and follow as many of those steps as you feel comfortable with. Really start taking care of yourself, focusing on YOU, and making yourself priority #1. As hard as it is (WAY easier said that done), try to make your WH your absolute lowest priority. Literally, getting your hair done or grocery shopping should be a MUCH higher priority than your WH. Once you start doing this, you'll begin to feel better about yourself, your health will improve, and you'll have the MUCH needed clarity to make educated, informed decisions on whether or not to even give your WH a chance at R. That is, of course, if he wants to, too, and is willing to go to IC as a condition of R, and fix his shit that resulted in this whole debacle in the first place.
The road is long, but all you have to do is just keep putting one foot in front of the other.
Be strong. Best of luck.