Not everyone who has affairs uses Whatsapp or even Insta. A lot use Snapchat because of the simple fact that messages delete unless saved.
Archived on WhatsApp only stay if archived. Most people go for the option of full delete.
Once the initial message has been sent and deleted to cover tracks, contact is usually a quick call or message that gets instantly deleted.
Some also say to the other person, please don't contact me, I will contact you unless they have an additional phone. Some do, and only use the main one to send pictures as the second phone is usually a basic phone.
I was on Tinder and Happn for a long time. I could easily just delete the app and quickly re-download without losing any contacts on there. Lots of the guys I interacted were in a relationship, some were upfront and mentioned this, even in their profiles (I didn't have contact with these guys). Others tried to hide it, but came up with various excuses and it became apparent, I lost count of the number of males in their late 20's upwards who couldn't have visitors because of the landlady.
A number of the guys who I chatted to over a long period of time, when I found out they were in relationships we had already become friends. Not emotional ones, not all I had met at this point, the ones I had fucked I stopped all contact instantly. And I am not condoning what any of them were/are doing, but I asked them how their partners never found out. They are really good at covering their tracks and do the above.
They use day rooms, whether with hookups from Tinder or Escorts (I now do this). Day rooms require no card details when booking, you book, pay on arrival and can pay cash. There's no trace.
Of course, the ones using escorts visit them and again cash or BitCoins. But again no trace. As an escort, I don't ever contact them. They contact me and they are very clear no contact and the initial contact is deleted and my name saved as something innocuous (once I find out they are in relationships I sever contact).
I do understand how difficult it is when lives are so intertwined. I was the owner of a garage when my marriage broke down and he worked there (when we first invested it was easier for it to be in my sole name). Plus kids and all the rest of it. However, I had to ask myself whether keeping everything entwined, an unhappy relationship, lack of trust and respect, having an effect on mental health, and well my self-respect so low to tolerate this crap, if it was all really worth it.
It was hard, I'm not going to lie. There were times I questioned if it was the right thing to do. Maybe I should go back. But I stuck it out, and when those doubts started to creep back I actually looked at life then and before. Obviously, he was still miserable, he'd lost a good thing. But, the children and I were a lot happier. It's also amazing how much living in a crap relationship where you are constantly worrying ages you.