I asked URWorthy to post because I thought you needed a gentle voice guiding you, that I, often, do not have.
I agree with everything she has said and I am sure that I will repeat a lot of it...
It is time to begin to get yourself together. Get a plan. You are way too worried about the what if's that you can't see past them...
The truth...
Your H may not be able to get a D while you are pregnant, but he can still leave. He can still leave to either be with the OW or be by himself. So that doesn't really matter much.
I don't believe that your R is really better when they have long separations, I think that you are simply calmer and that makes for better interactions.
There is no winner or loser in this situation. You don't win just because he stays and you don't lose if he leaves. Because you don't know what the reality of either of those situations looks like. Right now, it is all supposition.
They may have a wonderful relationship or a horrible one. You and he may have a wonderful relationship or a horrible one.
He may be a wonderful father to all of the children or not.
You may be happier on your own or you may not.
There is no crystal ball. No way of knowing until things acutally happen.
What is real right now?
You have a baby on the way and two daughters that you are raising.
You have a H that is checked out on many levels and there is NOTHING that you can do to change that, it is something that HE has to change.
Telling OW anything, now or later, will make no difference. She needs to figure things out on her own. Trust me, been there, done that. And the reality is, I was trying to scare her away by painting a picture of what my X was. Which eventually made me wonder why I wanted to be with him if he was that way. It was not done with any good intentions toward anyone, even myself. It was a way for me to cause the same type of pain I was experiencing. Which was me acting like the type of person I didn't want to be. Sure it made me feel good in the short term, but did NOTHING for my long term emotional healing.
What are you doing for you?
What were your H's complaints about you, his reasons for wanting to leave?
Are those things valid? Are there things that you can or want to change about you and how you interact with him?
Have you read DB?
Because you aren't implementing DB principals. What I see right now is you trying to power through this. Thinking that your strength and patience will make things get better while not acting at all.
What are your 180's? What are you doing to GAL? What is your PLAN?
"Acceptance doesn't mean resignation. It means understanding that something is what it is and there's got to be a way through it."--Michael J. Fox