First, I am so sorry that you are here. There is a lot of help for you in the healing library. Please go through it. Second, a story. Third, my advice.
The story:
My WH was having an A with a co-worker that had been ongoing for over a year. I recorded a call between AP and my WH (excellent sound quality - no way to deny anything and he did not) and he ended the A. 3 months later for reasons I don't fully understand (or care about at this point) the A restarted. My WH works very near our house and to enter his workplace you need a govt security clearance and the facility is surrounding by fencing, a gate, etc. Basically there is no way I can get in there and there is only one small area with picnic tables that is visible/near the road as the fencing is chain link there as opposed to solid. The A was (and had) largely taken place there at his work where there was no chance I would see them together but for that little chain link area. I drive by WH's work all the time as it is enroute to my bank. So one day I am driving to the bank when WH has sworn the A is over and done with and that he hasn't spoken to AP aside from when he has to at work when they change shifts, and who do I see but WH and AP sitting on the bench talking and laughing. They don't see me, but I am furious and pull over immediately like a block away and message him that he is a liar, I see he is sitting with her on the bench, and so on and he denies it, and tells me it was not AP but someone else and I am overreacting and being a "bitch." Like I am blind.
This can happen. Do not let it make you crazy. You're not. In my case I called the person WH claimed he was sitting with and asked them point blank if he was sitting with them and they said "No, he was out there with AP." I was not crazy. You're not crazy either. My WH and your WS are liars. That's the beginning and end of it.
To the extent you want/need hard and fast proof you can hire a PI or if you can't afford that you can do a few other things such as set her up. It sounds like your WS is similar to mine in that they are looking for opportunities to see the AP, so let them. Give them a perfect opportunity to do so. Set them up. It may be as simple as telling your WS that you will be away (I told my WH I was going to be about 2 hours away with a friend) and make it verifiable that you indeed are away if you can (we had a find my friends app on our phones pre affair so with a click he could confirm that I was where I said I was going to be and not worry that I would walk in). Then, before you leave, set up some recording devices (you can get pretty cheap VARs - in my case I just used my laptop) or you can confide in a friend as to what is going on and have that friend take photos or simply walk up to the house (or follow her when she leaves). The cheaters will be so elated that you will be gone they will take the opportunity. It may take a few times to catch them but you will. Your WS sounds pretty sloppy with covering things up so it won't take long.
Even if you have clear proof, your cheater may not confess. They may be angry and leave you or threaten to do so, obfuscate, try to convince you that you are crazy, have a meltdown, scream, or just give you the silent treatment. I saw the AP and my WH together with my own eyes, yet like some kind of comedy skit, my WH tried to tell me I didn't see what I saw. Proof will only get you so far.
The advice:
Get better proof if you need it for YOU, but proceed like you do know, because you do. You know. I would say that if you have decided you don't need more proof than stop playing the game with her and proceed like you know. If she is not going to talk about it, is going to continue to lie about it, you have nothing to work with. In that case you can show her with your actions you have no intention of rug sweeping this - and that until you get some confirmation from her, of the A, you really don't have much to say to her.
Even if you decided to gather more proof, think about what you need to do for you. You have said you want to R, but as others have said, you can't R with your WS right now - not if you don't want the A to continue, and not if you don't want this to happen again with someone else 15 years (or whenever) from now. You need to get yourself in the mindset that you may be on your own soon. I'm NOT saying that is going to happen, but you should plan for that. If you need to separate assets - do it. If you have financial issues that need to be resolved, do so. Find out what your rights and liabilities are where you are located if you were to divorce so you can start to protect yourself. Start thinking about taking care of yourself.
I can only tell you that I wish I had taken this same advice when given to me much earlier than I did. It cost me a lot of time and money down the road.
[This message edited by ThisIsSoLonely at 10:24 PM, Wednesday, August 2nd]