I can feel the cracks in the marriage

I (24m) am starting to feel my wife(30) pulling away and a divide coming between us. We have a 4 month old, and since this gift entered our life a distance has began forming and growing. Today my wofe stated she didn’t want to look after our son anymore. I tried to talk to her but she shut herself out.
Then halfway through the day she called me having a breakdown telling me she once again didn’t wanna do it anymore, I hung up, told me boss I had to go home and left.
When I got home I got our son to sleep and then we started talking, she kept saying she thinks I’d be better just divorcing her and that my son and I deserve better.
I understand hormones are still at large, and her whole life has been flipped completely, but I don’t quite know what to say nor do.

To then top it off, I sleep on the sofa and keep son downstairs to allow her to sleep the whole night through so she’s rested enough to tackle the day. I then wake up, keep lil man occupied until she comes down and then drive 2hours to site.

Another massive cause I believe for the cracks, the sex life has died down completely, maybe once a week, rare occasions.

Confused and feeling a little lost