What I'm about to say will sound twee but I really believe it's true - life WILL be better. You will look back at this time and it will be just a memory. A painful memory but a memory all the same. It will no longer be your everyday experience.
You will have a future and it will be happy and loving and exciting and optimistic. I know you can only imagine that reality with him but in time you won't feel like that. Right now it feels like you can't live without him. Though it also feels like you can't be with him either because he has treated you so badly that it would be terrifying to risk it happening again - how on earth do you move on from that? So where does that leave you? Ideally in a world where it never happened in the first place, I know. But that is impossible. So where next?
You need to continue seeking and accepting support from your family to stay strong and prevent the slip into depression from destroying you.
See your GP. Maybe more medication isn't the answer if it becomes a toss up between that and breastfeeding but they may be able to offer some other form of support.
Start envisioning a future without him. I know that's painful. You signed up for a family with mum, dad and children all together under one roof with shared experiences and happy days and it's been destroyed. He was also your rock through the tough times and losing that makes you feel set adrift. But there are other happy futures out there! I promise! You don't need to be in a relationship to be happy but most of us aspire to that so I will say it straight - you will find love and happiness again with someone else! There are lots of lovely, decent men out there. I'm not sure about you going on a date this weekend - you are far too fragile and whoever it is will be disappointing coz it's not him - so think carefully about why you would go on a date right now and what your reasons are. But when you are ready the world will be your oyster. Try seeing yourself happy in the future - imagine it and then it will become real.
I have friends whose husbands have just left. Some because of another woman, one because of depression. In EVERY case the women have met someone else and been very happy! The children are very happy. Their lives are good. Not what they planned but good. Meanwhile, (though irrelevant really), the husbands are miserable and unsettled and poor. You will be happy too.