I've been where you are right now. I know the complete and utter panic and heartbreak you will be feeling. I found all the messages 4 weeks before our wedding. I was a fool and went ahead with it. The marriage lasted less than 2 years. I hate myself for putting up with it for as long as it did. Yes, he stopped messaging. For a while. And then started again. A leopard never changes its spots.
Take time to work out what you are going to do. Be warned - he will say 'The Script' - "It didn't mean anything/ I was lonely/You never pay me any attention" - all lies! Because that's the only language they know- lies.
My heart goes out to you. But please, whatever you do, maintain your self-respect and know your worth. I thought I knew my worth but put up with so much it turned me into someone I didn't recognise, my self-esteem was absolutely on the floor by the end of it.
It's been 5+ years since we split. It took about a year/18 months to completely get over it but wow, I never been so happy! The relief when I finally chucked him out cannot be put into words.
I see him now when he picks our DC up and feel NOTHING, not love nor hate, just NOTHING, like those years never happened.
Take care of yourself. Lots of good advice has already been given by PPs on what to do right now. The main thing I'd try and do if at all possible is to delay him coming home tonight. You need time and space away from him to let it sink in in the interim and to work out what to do next. You're lucky to have your mum with you. Good luck and stay strong. You WILL get through all this. It's shit right now and will be for a while but you WILL get through it.