The 53-year-old actor, who said to be smitten by Theron, 38, has moved in with her, reported Radar Online.
"Sean is head over heels in love with Charlize, and her son Jackson. He is a totally different person around Charlize. The two began talking about marriage in the last few weeks, after Sean moved into Charlize's house," a source said.
"She has never wanted to get married, but seeing how Sean interacts with Jackson, she is having a change of heart. For the longest time, Charlize thought it was just going to be her and Jackson, and she was ok with that," the source added.