I was never in the exact same position as you, let alone with the responsibilities that being a parent entails, however here's my tuppence for what it's worth. Of course feel free to take it or leave it.

Relationships ending tend to fall into "really easy" through to "nigh impossible". I was recently the victim of the latter where my partner left me, and I would be stupid to deny that it has really broken and changed me.

The thing that made the biggest difference to me, was accepting that the end result was that I was not going be with them again, and that I needed to emotionally detach myself from them. I'm still working on it even now, 6 months later I still love them in a small but painful way.

When a person you love does this to you, they take a piece of your heart with them and it hurts a lot. It will never heal completely.
The horrible reality is that you need to accept that you will change as a person, you will learn and you will grow when this is finally done. It is one of the most difficult things I have ever had to deal with.

Keep holding yourself together, keep your friends and family close, you can do this, it will get easier.