hello Poshaubrey - lovely to see you, but sorry you are having to cope with difficult news at the moment.
The question you pose is a very tricky one, - so hard to make these kind of decisions. I think it all probably comes down to what you think will be best for your DS knowing him as you do, and the sort of child he is.
My DD was 18 when I was DX, and just about to go to Uni. She wanted to delay going, but I was very firm that she didn't change her plans for me, so she went. In some ways I'm really glad she missed me having chemo and being pretty ill as I know she would have worried, but on the other she says she felt cut off and worried not being here, and perhaps being able to actually see me would have been easier for her. I don't know.
If your DS goes to boarding school, would he be back for weekends etc fairly frequently?
I suppose in a way with a young child it might be easier for him to continue to get on with his life doing little boy type stuff in a community away from home, if you are going to be going through treatment.
Aargh - I don't know - I'm being fairly useless here, and obviously you and your DH will have mulled all these arguments over in your head too.
What does your DS think - does he understand the reality of the situation (I know there are no definites obviously) what would he prefer?
Does he have a strong support network of other adults (grandparents aunties etc) and other kids in the home setting? - I think I might be reluctant to tear him away from that if so.
I think somewhere inside me there would be a little voice saying that horrible as it is to see someone you love going through treatment and being ill, somehow being cut off from them is worse and more worrying.
Hopefully someone less useless than me (and with DC in a similar age bracket to yours) will be along soon with other suggestions 