Think of immune system strength as going from 1 to 100. Your DS has a strength of 1, essentially. You really need to quarantine DH away from you and DS, if you’re not sick yet, and if that’s possible in your house, and keep DH in just one room. So, no, don’t share a bed, and no, no cuddles. If this is evolving norovirus or something, the only thing that kills it is bleach, so having your DH wash his hands before cuddling DS would not be enough at all.
Now, with that said, you mention DH has an upset stomach and diarrhea. Do you mean he has diarrhea and vomiting? If so, yes, quarantine. Keep DS away. Wipe all surfaces and handles (door, toilet) down with BLEACH-based antibacterial spray or wipes (Domestos does a bleach spray I believe or you can just mix bleach and water in a spray bottle) as regular antibacterial sprays will not kill norovirus (just in case that’s what you’re facing). If you have two bathrooms, just “give” him one bathroom and you stay out of it for now. IF he just has diarrhea and his stomach feels unsettled, there’s still a chance something he ate wasn’t “good,” and he won’t be sick in a contagious way. Unfortunately, it may be impossible to tell, so I would err on the side of caution. If he doesn’t vomit, though, it’s somewhat less serious.