Welcome to SI and sorry that you're joining us. There are some posts pinned to the top of the forum that have a lot of great information and we encourage new members to read. There are some other great posts that aren't pinned, so you may have to scroll to find them. They have a bull's eye icon. The Healing Library is at the top of the site and is another great resource.
Perimenopause may have had an influence, but it isn't an excuse. She could have done a ga-zillion other things, but she decided to cheat. If her friends are so Pro-D, why didn't she D you before cheating?
If you can, IC for you both. Once you're on your healing path, then MC might be helpful. Your M didn't cheat - your WW (wayward wife) did. There are some MCs that will shift part of the blame to you and you didn't cause your WW to cheat. She made that unilateral decision all on her own.
Your WW should read How to Help Your Spouse Heal From Your Affair by Linda MacDonald. It's a nice blueprint for her. Another good book is Not Just Friends by Dr. Shirley Glass.
If you haven't been to your doctor already, you both should be tested for STDs/STIs. There are some nasty diseases out there. If you're having trouble eating, sleeping, or depression, talk to your doctor for some meds. They can help you through this rough patch. Healing is a marathon and not a sprint, so be sure to take care of yourself during this time.
BW M 34years, Dday 1: March 2018, Dday 2: August 2019, D final 2/25/21