"I did. You lived in this small studio apartment for a while." And she'd hid him when Black Widow had come searching for him. He hadn't been ready to talk yet, and Mia understood hiding from your feelings for a while.
"That's what you told me." She replied. "If you lied about that for some reason, the reason would have been yours. I took you at your word and never suspected differently."
She knew this was confusing, but she was banking on him remembering her clearly enough to know she didn't lie.