be the gofer / the driver if he says we need to go here to collect this, say I'll drive, or I'll do that. Order or cook food without being asked to when you see that meal times have gone askew. Just be there physically ie go over to the house and hang out, but dont expect conversation or interaction. Do the washup or load the dishwasher after meals. Take the garbage out, take the dog for a walk.
When my dad died, my friends backed off. After the viewing we had neighbours and family back to our house and I invited one friend. She said she couldnt as her boyfriend was with her. I said he can come too and she said no he wouldnt be comfortable. I really needed someone there for me, to ask how I was, to just sit and chat. But I ended up being the hostess, making sure auntie had a cup of tea, uncle had a beer, my mum had a sandwich etc etc you get the picture. There was no one there just for me so even though we had just come from the viewing and my head was in a spin, I had shut all that off and be the hostess.
You dont need to be anything, just physically be there, even if you just sit there in a corner playing with the dog. He will really apriciate that someone is there, just for him, someone he dosnt have to put on a show for, take care of, do something for. Be there person he hcan just come over and give a hug to without having to say anything, or someone he can just sit with without having to speak or have anything expected of.