To be honest his son not coming home to eat his tea wouldn't have bothered me.
I'd just cook enough, if he eats fine...if he doesn't that's fine. If him not not coming home was a regular thing, I would just cook for those in the house at the time.
You made the issue about his son, so his response was to take his son out of the equation and you were each responsible for your own children.
Why did you feel the need to tell your son what his child was getting? I would find that annoying as well, but it's just the final straw. The relationship seems to have had some difficulties and not been great for a bit, so it's probably for the best.
You'll need to figure out the finances and how to house yourself and the boys, but don't be pushed out before you're ready.
A 16 yo would know better than to ruin the surprise...16 NOT 6.
I would not be begging him. Just try and be positive about the future whatever that may be.
I think he's decided to do what he feels is best and will have no problem moving on.