Like many members of the struggling British outfit, Boullier admitted to feelings of relief in Singapore that the Honda divorce is now set in stone.
"It had become inevitable," the Frenchman told Belgian broadcaster RTBF.
"After three difficult years, important decisions had to be made before it was too late. Now what we feel is relief but also sadness because we built a good working relationship with Honda even if there were no results," Boullier added.
Boullier said: "We have information from Renault that proves to us that their engine is competitive.
"Maybe it is a bit behind the Mercedes and the Ferrari but it has potential."
"We have had meetings that show they are working on a reliability and performance package that will be more competitive next year.
"The other advantage of working with Renault is that we will have a say in engine design. In 2019 we will have a solution that is almost 'factory', so it's an advantage over a customer engine."
McLaren are currently in ninth place in the 2017 constructors' standings.