This is an idea that Steph suggested.

It was an act. He had to keep reminding himself of that. She'd dropped into his life like a bomb, and was about as dangerous, but it was an act. For them to get out of the situation alive, they had to pretend to be dating. Pretending got out of hand when she kissed him.

Then she walked out of his life, and all he could do was say goodbye to Modesty Blaise. He didn't hear her saying goodbye to him.