Everton
I think that doing the two together, as EcoMouse said, will be too much for him to deal with.
And to be honest, it's unlikely that he'll get past hearing that 'mummy and daddy aren't going to be living together anymore'
You need to tell him the intial 'news' and take it a step at a time with him, gaging very carefully how he reacts.
Honesty is the best policy and children often surprise you at just how much 'fact' they can handle but you need to tread carefully with him in the early stages of this.
He will be very upset but might not cry, on the outside at least. As Eco says, he may well shout, ask why alot etc....
Take the time to explain in very simple terms what is happening and will happen in days to come, not weeks and months.
Remember that on Saturday night, when he went to sleep, everything was fine.
He wakes to be told that everything he knew last night is about to be different to one degree or another.
Don't rush into telling him everything all at once.
Give yourselves time to adjust to this as a family.
Good luck x