The French actress addressed rumours in an Instagram post.
"Many years ago, I met the man of my life. He is my love, my best friend, the only one that I need," she said.
Cotillard also revealed she and her husband Guillaume Canet were expecting their second child.
The 40-year-old's private life had been thrown in to the spotlight following the news that Jolie had filed for divorce on Monday, citing "irreconcilable differences".