Partner with secret Snapchat account

What to do....

When my baby was 5weeks old I found messages on my partners phone from another woman. I confronted him and he admitted that he was feeling overwhelmed by his life as a dad to a newborn and needed someone to talk to. The messages were nothing to do with talking, but more suggestions of sending naughty snapchats and catching up for a drink. At this time he had also downloaded tinder, which is where his conversations started with this other lady.

We stayed together, with him promising to never do it again etc. we got married and all seemed to be going ok.

Fast forward to tonight, bubs is now 10 months old. On my Snapchat I notice an add friend suggestion, hubbys initials and birthday as the username. Instantly I was suss. I go into his emails and there is a welcome message from Snapchat, from about 15mins before. I check the emails a while later and it has been activated and is now in the deleted folder. I get bubs to sleep and try to get to sleep, but send him a message asking about the account. He is completely denying all of it, the email is now deleted. Says it never existed and that he has no idea what I’m talking about.

So I have now logged into his Snapchat after changing the password and he only has one friend on there, added same day as account created and 5 snapchats sent to her.

I have told him I know this, he is still denying all knowledge.

EDIT - I sent the chick on Snapchat a message, she said he had been messaging her all day on POF and then they sent a few snapchats that night. She was going to send me his profile on POF but it had been deleted. She told me a few things he had said which were spot on to last time he did this. I confronted him again, he is still saying it was not him and is now saying it must be someone else that has set up the profile on POF and the Snapchat account, he is currently accusing his ex’s sister, who he claims to have randomly seen a couple of weeks ago... he has now deleted all social media from his phone as he says that’s how they got his information. He has given me full access to his phone, I checked to see if he had the POF app, but it wasn’t on his downloaded list, but neither was Snapchat, which I know he had. And from the google searches I did any apps you download show up on the list, even if you have deleted them off your phone.

After writing this and adding the edit I am feeling really stupid for not kicking his arse out already!!
Any advice from the sisterhood would be great.