I truly understand what you are feeling - I have felt it too. When I finally came to accept that there was no coming back for him (I had to close that door for myself, though he had never given me reason to leave it open), it was a time of a new wave of grief. But it passed in time and things got better.
My H started going to church with OW about 6 months after he left. He was still married to me. He explained to the pastor about their situation. ANd the pastor welcomed them! I asked to speak to the pastor because I wanted him to know that I was standing for my M. He would not speak to me. I have never got over that. And H and maggot sat in church every friends around my friends and clients, some asking H if he was still married to me and him replying YES!
I am referred to as "Your Mother", which is even more estranged in my opinion. But I know the intial sting when it became apparent.
I think that we put on rose coloured glasses and try to keep the good memories alive while we are DBing and trying to save the M. We stuff the bad memories out of the way and live with some denial. This is not such a bad thing at the time, some of us could never have coped at all without some hope (false or real) and some denial. But reality does slap us in the face at times and we're faced with what is really going on and boy does it hurt! And another round of grieving begins. And then you re-evaluate. And that's that part you need to do on your own. Because only YOU know the whole story, all the feelings, the nuances, the little things that were said and the undertones. And you decide what to do next. Or not - and you let fate decide for you.
Mermaid, my H has been gone for 5 years and there is not a day goes by that I still don't think about how nasty and cruel it all has been. How unfair. How some of the people you thought would stand up for you and your marriage fail you and how others didn't.
I guess the best you can do for your Ds is to continue to be their loving mother. Reassure them that life will go on. Don't mention a future with daddy. Just make sure they know that you will always be there for them. And don't send messages back to him via them.
None of us knows how long these MLC relationships last. I'm sure there is a lot of denial at my ex's house. But guess what - there is a calming peace in my home. It was never here when he and I were together. That tells me a lot.
I've rambled and I'm sorry but I wanted to let you know that I care and I've been there and you will be fine. Just keep living your life to the best of your ability.