Hi Mandy & welcome to mumsnet :) the honesty on here can be a bit startling if you're not used to it but you will have comments from people with a range of experience.
I think that it sounds as though the emotional affair did not end. Instead it escalated, he left, he went to the OW (other woman), she wouldn't let him stay so he begged to come back. He came back, then she changed her mind & now he's gone back to her again. I'd think that he has not left her ever, regardless of what he has told you. I'm sorry. Perhaps the change in dress/values are down to her as well.
So put him aside for a moment & think about you want. Stop letting him decide whether he wants to come home or not, you deserve more than that & he doesn't get to decide what happens to everyone outside his selfish little bubble. What do you & your child want?
It can be a crippling betrayal, especially if you didn't see it coming but try to focus on your future. Plenty of women have post-affair happy successful lives. If he has now ended your marriage then he can't come back, even if he wanted to as his treatment of you is disgraceful & cannot be condoned.
If you own joint assets, such as house then may I suggest you consult a solicitor (or the CAB who are free) & think about whether you want to start divorce proceedings. Access to your child also needs to be agreed.
I know its hard, but try to take control & show him that you won't put up with his shit anymore. Now that he has gone you no longer have to feel responsible for his happiness & never never blame yourself. Nobody forced him or 'drove' him to an affair, it was all his choice & look what he's lost now