How to still have a relationship with toddler while having newborn

I want to start this by saying I hope no one comes to read this with judgement. But…

I have a three year old autistic non verbal son. He is my whole life. Of course when I first got pregnant I did not know he had autism. The diagnosis came around 5 months pregnant. My son is attached to me big time. We cosleep and basically spend 24/7 together.

I tried to explain to him that mommy was having a baby. But I don’t think he understood. Well fast forward to giving birth. My newborn is having bad reflux. I didn’t bank on having to hold her majority of the time.

I’m lucky to have good support but I’m grieving the relationship I had with my son prior to having baby. I miss when it was just us. It gives me bad mom guilt. I cry all the time over my son and also my daughter. And feelings that I’ve somehow ruined things for him. I try to give dedicated time to him and he seems okay besides spending some more time in his room. And he seems a little distant from me which actually breaks my heart.

At night I put him to sleep if the baby is content and then my mom or husband sleeps the rest of the night with him.

But I sit out in the living room crying because I want to be with him too.

Did anyone on here have something similar happen as far as feelings regarding your first born? How did you move past it?