Hi ceilingwalker, so sorry you have a reason to be here, but glad that you found SI.
How does one know, is there a test of some sort to determine someone's remorsefulness?
There is, and your WW is failing it. She should be doing everything within has power to prove to you that she is maintaining No Contact (NC) with the other man (OM). She should maker her life transparent to you in order to provide you with comfort that it is safe to "Not Divorce" while you decide what you want.
She should be seeking out individual counseling (IC) and books to figure out why she found herself in the position you found her in.
To be honest, it seems to take wayward spouses (WS) time to get from being caught to being remorseful (if they ever get there).
I think you may be early to think about Reconciliation, and for now you might be better focusing on what you need to “Not Divorce” her for the time being. What boundaries do you need in place to feel safe enough to stay while she tries to figure things out, you heal, and then you can both work on your M if you are so inclined.
A start would be the transparency I referred to above. You should have access to her phone text, and use records, her email accounts, and bank balances. You might ask about the whole story, surly the OM in bed was not the first time. You mention the red flag behaviors existing for a long time, what about the As? My wife had 4 OM (that I know of), over a period of years.
You said she says she will not do it again, but why not? She should be able to provide her reason for having an A (and it was nothing that YOU did or did not do). Once she knows why she had an A, she can work on changing her behaviors and beliefs that led to her having an A. Then, and only then, can she really begin to say she will never do it again.
You may want to attend some IC for yourself to help work through your emotions post dday, but I do not believe that marriage counseling (MC) can be of much help this early on. It was not the M that was broken, it was your wayward wife (WW), and she needs to be fixed before MC can help. Until she understands why she had her A and stops thinking in wayward modes, it is hard to get to the real problems.
While you are setting your boundaries for your WW, and watching to see if her actions say she wants to stay M to you, you should take time to protect yourself. You should have an account of your own like your WW does. You should find opportunities to get finances in better order (pay down bills, build up savings) in case you decide you do want a divorce.
Finally, do you know who the OM was in bed? If not, she should tell you, another good requirement to stay and not divorce. If he is married you should let his betrayed spouse (BS) know. Do not tell your WW you are going to tell, just do it if you can.
Best wishes to you. SI is a good place with great advice. When you get the time, come to the Betrayed Men thread in I Can Relate and say Hi to us there too.