I accidently proposed...

He's been with his gf for 9 months, they’ve lived together for the last 2 months. To commemorate their 9 months he takes her to a fancy dinner and gives her a ring. It was a diamond but a small one that his mom gave him. So he’s not thinking anything about it. Until he pulls the box out at their fancy dinner and she yells YES! People clap, she’s crying and he can’t believe what’s happening… he say’s he’s sick about it but now he can’t take it back. She’s already called her friends, she planning… what is he gonna do?