It's really difficult. I did it, but quite badly, I now see.
With the benefit of hindsight, I would say just accept that they will come first and that will never change. It's the right thing, but is quite difficult.
Holidays will be spent doing child friendly stuff,and social occasions will be missed because of contact weekends, ferrying to sports , parties and so on.
Be kind and generous and non judgey in your dealings with them. Other people's children are easy to moan and bitch about, but remember they are children and none of this is their fault.
It might also be useful, if you do move forward, to discuss your role with the children. I always felt caught between a rock and a hard place as I felt I ended up with the life changing stuff, but with any views I had being ignored as my husband just wanted the dc to be happy.
Like I say though, looking back I was a bit of a bitch, really, at times. I really regret it. In my partial defence, I had a weird childhood myself, and was a career focussed person with absolutely no experience at all of children!