If it's my post you are referring to, OP, I didn't say you were weak for staying. I was responding to another poster putting a value judgement on the strength of your marriage because you were staying.
It's not weak to leave and nor is it weak to stay but decisions to stay shouldn't be based on fear of being alone or losing a comfortable situation. How could that ever work in reality? All that would happen is that the betrayed spouse would tacitly accept the cheating and from that point, be unable to function in the relationship as an equal partner.
The OW and her husband are not your business really. Posters have cautioned you about taking this up because a) you may get a scenario where OW was wanted by both - her husband and yours - and how will that feel? and b) it's vengeful and reduces your behaviour to an even lower level.
This is two years on. If you really felt that the husband should know - from the position of knowledge to benefit him - you would have told him then. Telling now would in no way benefit him and may open a can of worms that you really don't want. Take your shot then and accept the consequences of your own behaviour which would be based purely on spite.
I can hear your hurt, pain and frustration at the 'scot free' aspect that you imagine but healing yourself is the only thing that matters and your continued focus on somebody who was no part of your marriage, as opposed to the one who was supposed to be firmly signed up to it, can't escape you. How can you go on with that ever-present thought niggling away at you all the time? For your sake, close that door soon.
If you want to stay in your marriage then that is your decision and I hope it is your husband's focus too; he should be putting in the time and effort to reassure you that your decision was the right one. At no time are you obliged to keep going with it though, however much effort he puts in. He changed the rules. He did all of it. This OW? That OW? Any OW... all of them powerless without your husband's willingness to engage and deceive you. That is the point that so many are making, because it's true.
I really do wish you peace in your journey OP; this is a horrible situation but ultimately, only you can make the decision to let it go now and have a totally honest agreement to commit to your marriage with your husband - or to keep carrying this with you and living a half-life.