I haven't been through this personally but wanted to offer my support (not many folks on MN after midnight usually)
It is very hard to move on when you feel like you don't have closure. You feel wronged because you're being accused of things by his family and you probably realise how pointless it would be to try to get them to see your point of view as he has obviously brainwashed them in order to justify his cheating on you.
I think you need to be really kind to yourself and consider getting some advice from your GP. He may suggest a low dose antidepressant (nothing to fear, you can come off them after a few months when you feel like you're coping better) or some counselling, which he can arrange for you.
Are you getting support from your family and friends? Some people think that after a certain time we should be "over" traumatic events, but it's still very new or you, and obviously very painful. In some ways when a partner leaves you for someone else it's worse than a bereavement, because although it turns your world upside down they're still there and they betrayed you.
You do have the strength to get on with your life, but you need to give yourself time. It wasn't your fault you had PND, and it was no excuse for him to go running to another woman (he took a vow to stick with you in sickness and in health) so don't take responsibility for it. He did it because he is a shit. Let the anger carry you through this patch until one day you realise you don't care any more.
Perhpas once your decree nisi comes through you can try to have a fresh start, perhaps a new haircut or a new excercise regime to make yourself feel better, and put him out of your mind as much as possible (wear an elastic band around your wrist and snap it when he enters your mind!)
This will get easier. You just need to take each day at a time, as the old cliche goes.