YANBU
if you have no help he has to stay.
but if you have people who can help out.
you gotta tell him the choice is his.
otherwise if you ever argue about anything this is one of those things he'll cast up for years to come. that you forced him to stay.
he can use it in ammunitions in arguements for finance/parental responsibilities/etc,etc
you never know, if he's here to see them enter the world he will probably change his mind anyway as soon as he see's how difficult it is with 3 so close in age.
it's better for him to decide on his own accord to stay.
if he decides to go then you have ammunition against him for years to come . lol.
perfect excuse everytime for some you time away from the kids.
and also, . . . i am sure you would deserve a large present for being left on your own. specially if he's doing it for the cash
my friend was in a similar situation..
she managed to get a girlie spa wkd (guilt free as she had done her fair share) and an extra diamond on her engagement ring!