OP when I found out that XH was in contact with OW in the period before he moved out I was like a woman possessed. I would grab his phone, take it to the toilet and check messages / call history. I checked his emails.
Then I used his phone to block her, so he just got a burner phone (which I found out by going through his emails). So then I would take his car out to "go shopping" and then go through the car looking for it.
It drove me insane. It was so so unhealthy, but it was like a compulsion, like I was craving some control over a situation I had no control over.
So I totally get it.
I realised that it didn't matter what he did / I did / what I found / didn't find / how long they spent on the phone on his commute / how many messages he sent etc etc ultimately his betrayal and my lack of trust meant that our relationship was dead in the water.
I made myself stop doing it as, like you, my anxiety was going through the roof and it was a vicious circle, and once I did, I was able to move forward, separate and my anxiety subsided.
It is a couple of years on and from time to time I still find myself looking at their Facebook profiles etc, but I am in a much better place now.