I am so sorry you are hurting. I know right where you are.
Gently, kids at that age rely on non-verbal cues. He is watching you all of the time. For guidance, reassurance. You are in a great deal of pain right now and he is mirroring and/or reacting to it.
My youngest was 18m on DD. After a sleepless night I went in to wake them the next morning. I had my best fake smile on and put on a great show. My then 4 year old bought it and was really happy excited.
My then 18m old kept looking at me with this perplexed look on her face. She did it for several weeks. She got really clingy and her behaviour changed - she was stressed and angry.
These were not her emotions over what was going - she was picking up on the tension and my very very raw state of mind at that time.
As you said he still has a daddy. He will likely get more/better quality time with him (in an ideal world).
You can't see this right now but life is so much more joyful when that drama/tension is removed. Again, in an ideal world both parents really want to invest in quality time with their kids that was taken for granted when we're with them 24.7.
I am a far better mother in S/D than I was in the M. Because I appreciate these amazing little girls and my precious time with them. Because I'm no longer in crazy-making limbo land. Because I am not being emotionally abused nor am I rugsweeping/gaslighting myself.
I am free.
It hard to deal with our children's pain whilst feeling like we are dying ourselves. It is very important to not interpret their emotional or verbal expressions through our lens of pain.
Easier said than done - I still struggle with this myself.
He deserves an intact, safe home. I feel I'm failing him. I failed him by not choosing a better husband and father.
I've posted this many many times myself. Reaching acceptance has been painful but essential.
My little family is intact - more intact with this new composition than it was when we were 'intact' in the traditional sense. I'm still working on hating myself for choosing so poorly. That is going to take a little longer to get through.
((BrokenDaisy)) You have been through the worst of it. Now is the acceptance/rebirth phase - I won't lie, it is enormously painful. More painful than anything else because I no longer had 'hope' to put on my wounds as a bandaid.
But I will say I came out of it..... I don't know how to describe it. Clean? Light? Bendy? It was a seismic change. I was no longer a tight ball of twisted rubber bands and I have seen a huge difference in my girls.
Lean into the pain when it gets bad. Please know it won't always hurt this much.