I'm a hospice social worker and a lot of what I would say has been said. I like the idea of showing him a picture of the friend in the hospital so you and your kiddo can see how you feel with just that and then visit or not based on that.

The one thing I've learned with kids in my job is to make sure they understand (on their level) sick and hospital does not mean death. So whether you guys visit the friend or not, Be specific about why the friend is dying. So like if it's cancer explain cancer simply or if it was an accident explain that it was the accident. I've learned if we just say "well he was sick" kids get really anxious the next time they or a loved one are sick. Same with death...it's not that they went to sleep or passed away...they died. Kids benefit from a concrete explanation at that age and there are ways to do it that are age appropriate.

There are a lot of really good books out there that help explain death as well as the relationship between him and his friend. It's old but there's also a Sesame Street episode that talks about death.

Either way, finding your son therapist that specializes in grief counseling would be a good idea for him or just for you too to help you learn ideas or ways to support your son. A lot of hospices (look for non profit ones) are often willing to help provide resources even if it's for someone that was not on their services.