The cause of Alfredo Sauce breaking is because of the butter separating from the rest of the sauce.
The butter separating from the sauce and causing the Alfredo Sauce to break is usually because the heat was too high or you have scorched the whole milk which caused it to separate.
So when making Alfredo sauce you should turn the heat down so that the milk does not scorch and then it should not break.
When you're making Alfredo Sauce and Alfredo you do not want the Alfredo Sauce to be boiling because if it does then you have a problem with the sauce breaking.
You want the Alfredo to simmer but not boil and if your Alfredo sauce is boiling then you have the heat on too high and should turn it down.
Turn the heat down on the stove before the Alfredo Sauce gets to boiling and it should not break.