I'm sorry for your loss doesn't really cover it, but my thoughts are with you
I lost my mother just under a year ago and whilst it wasn't completely unexpected it* came as a shock as we'd been to see her earlier in the day and whilst she was very ill it wasn't much worse than she'd been several times over the previous month.
My only advice is to try and remember the good times, it's hard and the oddest things will remind you of him**, but try to continue with your life as that's what he would want and every now and then possibly try and do something you enjoyed together, when your little one get old enough share the memories of his grandfather with him.
The pain does get better, or at least you get used to it to a degree but it will hit hard at times (I'm struggling a bit with this post:/)
If your mother is still around try and spend time with her, I know it hit my dad really hard and the only people he could even talk to it about were close family and in our case the sharing of silly stories about what had happened in the past helped us a bit.
*She'd had dementia and had been in and out of hospital several times over the previous month.
**I.was getting iceblocks out of the freezer and it hit me, as we used to go camping when I was about 10 and every morning my mum would pop down to the site shop and get the other set of iceblocks that had been frozen overnight, or when some TV show unexpectedly plays a bit of music she liked I remember her singing (badly
) along to it whilst cooking.