Good grief OP! I've just got in the house and peeked on Mumsnet and saw an update. As a few days had passed by, I assumed all was well and you had found nothing untoward.
I am so sorry that this was not the case.... that it was something so horrendous... what a bloody shock.
I hope you can take some time off work and other everyday stuff to process this and to basically breathe! Go and see your GP... or at the very least, get an appointment with your local sexual health clinic.
This is so horrible, my heart really goes out to you. Like you, I only found out by checking the Google Activity which is permanently stored - and generally by default unless the user deactivates it. That is where I saw the dodgy dealings, the searches for sex clubs and the dating sites. So sad, but I would not have checked at all had I not also seen something that he had lied to me about, a fake FB, multiple fake gmail accounts for the fake FBs, of which in the end, there were several. Fake Instagram, Lord knows what for, but so many fake profiles and all denied, that I knew there had to be something else going on.
It is good that you know, better not to keep living a lie. You will feel as if the rug has quite literally been pulled out from beneath you... I know I did... but you WILL be ok eventually... I think the initial shock is horrendous... what came after it for me was the anger at my wasted time and energy.... but that anger is incredibly motivating.
I am sure you will continue to get support here and I am glad that you have good friends in real life.
Sleep well if you can OP.