Sorry, I've done my first two posts here on mobile, got to my desktop, where I feel like I can type more.
Your BW is going to want information about the affair at some point. One suggestion that I have for you is to put together two timelines, one of them is a more general, 1000 ft view of the events, and the other one is more detailed, and has a bit more of the details about the meet ups, etc. You can share with her, both timelines, the more detail heavy and the less detailed one. Let her decide which one she wants to have. There is a caveat, once a BS hears the sordid details of locations, times, sexual positions, any kinks you might have explored, etc, they cannot unhear them. So, it is best to put that level of detail in the "detailed" timeline and keep that stuff out of the other. Every BS is different, some of them hear those details and have mind movies that they cannot purge, others are just fine with it and sometimes feel like they need those granular details to heal.
The timeline is an important piece that your BW will need to understand how it all happened, and put some context and clarity to the events of the affair.
As I also mentioned, it is time to look at the Help Wanted ads. I take it based on your use of "mummy" in our introductory post that you might not be from the US, where Covid is still raging along. I would still advise you to look for a job here in the US, but of course good jobs are going to be harder to come by with Covid and the economic fallout that has accompanied this pandemic. So, start looking for a job and finding a way out of the job with your AP. Your BW will never be able to get off pins and needles with you still working with her in any capacity. Maybe you are able to work something out with your boss in the interim to avoid her entirely, but long term you or her got to find new employment. Since you cannot control your AP, you get yourself out of the situation where you could have continuing contact with her.
I would really look at the readings suggested by the board here. I know that reading them helped my wife and I both with our recovery. It helped us to understand the pain that we had put each other through and also how to take steps to try and rebuild trust. This is a long journey and reconciliation is a gift given to Waywards, so you have to prove to your wife that you are a worthy recipient of said gift. That will take more than words and a few actions.
If you haven't already given your wife full transparency on all your accounts and devices, I would suggest you do so right away. Another thing that my IC suggested that I liked, was be deliberate about your actions. When you are going to the grocery store, tell her, "I'm going to the store and I expect to be back in 30 minutes." If you are running late on the trip back from the store, let her know that you got held up at the checkout or something like that. She will be able to verify your location with you sharing your location, and also a receipt for the groceries with a timestamp. By being deliberate about your whereabouts and your communication, you are showing her that you care about her and you want to be honest with her. Keep in mind, that you haven't been honest with her for a long time, and while this exercise may seem a little bit over the top, it does help.
One thing from your initial post that I want to correct, you said that this was the "biggest mistake of my life." I'm not attacking you outright with this, but that is not the right approach and framing to use here. A mistake/accident is something like dropping a glass of water on the floor and having to mop up the spilt water and the sweeping up the broken shards of glass. Affairs are not in the category of a mistake. Obviously, I would have to know more about your story, but given that you work with your AP in some capacity, she didn't just slip, fall and land on you while both of your clothes magically flew off in that same fell swoop. This was a series of choices that you made little by little over approximately 2 years. I think you get the picture, I'm not on my high horse, but I want to be clear, affairs may be something that we feel are "wrong" and a "mistake" in the aftermath, but they were something that in the moment we gave ourselves permission to participate in.
Your IC will be important that you get in and figure out your Whys. Why did you give yourself permission to pursue a relationship with another woman. There is something about your past that made you feel that it was alright to pursue the feelings that this AP caused you to feel. It was less about the AP, but more about what she represents. Your IC should be helpful, as long as your are honest about the past with them. Also, if the IC tries to blame your marriage, I would find another one. Your wife is 50% responsible for the state of your marriage at the time of the infidelity, but she didn't cause you to cheat. We as Waywards 100% the cheating part of that equation. Some ICs will try to put the infidelity on the Betrayed Spouse, and that isn't a recipe for success in therapy.
Good luck and keep posting. The group here will be available to help you as you push through this and work on yourself.