Hi , welcome
I feel for you.
Firstly, you forgave her for the first affair, think you're punishing yourself too much by hanging onto those rocks- gotta chuck them in the river eh. Beating yourself up is not good for your health.
However your gut instinct lately might be spot on so all you can do is keep an eye open and if real doubtful use a PI. Again you need closure and all that is part of your mental health needs.
I've had 4 long term relationships all over 7 years duration. So 3 times now I've gone through the grief process. Believe me life goes on if you part ways and it can be a very good life, just very different. So if that happens let the process go its course and kick start your new life with some positivity ok.
Finally, I've openly admitted with my dysthymia (long term depression) that I've cried through life. From an ex prison officer and dog ranger, security, big guy, it hurts to admit it, but its the truth...so please dont feel embarrassed.