Belle didn’t leave just because he was spinning gold. She left because he wasn’t honest. 🙂 He has never told her about why he needed magic and what he intends to do. He keeps her in the dark due to shame and trust issues, I think. She told him he needed courage to let him in–all she wanted was answers.
But I do agree the breakup happened a bit too quickly–I would have liked Belle to know about what happened to her father and why her posters didn’t work. That would have created a really interesting setting as to whether or not she can forgive him and move past it and all. Though I think that is mostly due to limited screen time–they only have about 45 minutes for a story.