Op, I spent about four years feeling "I deserve more than this" (for different reasons) but I was paralysed and didn't actually leave. So, nobody who's left a marriage expects you to pack his bags the first instant he gets a text from a female you don't know about! But all of the new information and the new clearer way of interpreting it will be chipping away at your denial, I hope. I think we steep ourselves in denial because we all fear change so much.
You say you are afraid of being a single mum. Well, it's a bit adjustment alright, but what I would advise you to do is to really look into being a single mum. The logistics. The practicalities. What forms to download. What FIS you would be entitled to. What childcare arrangements you could make. Would you move, would he move, calculate maintenance on the online calculator.
This is boring bureaucracy, and it make take a week to get through it all, or more. But you know what, if you have it in your head that actually, maybe, maybe if it comes down to it, and if it's the choice you make then yes you bloody well will get through it and get through it happy, then it will give you a bit more power in your discussions wth him.
I always think that in negotiations with men who cheat/want to cheat, if they know that your bottom line is that you're afraid to end the marriage because you fear being single more than you fear having a cheating husband then you just have nowhere to go.............
so do some research, just to bolster yourself up. You could if you needed to, be a single mother. That's not the same as saying LTB. Just believe it. You could do it. And it would not kill you. Just make sure that you believe that when you are demanding more respect from him. If you don't believe that then it's unlikely that he will give you the respect you deserve.