I don't think Buffy was quite rational enough to be drawing that conclusion.
The fact is Buffy was emotionally vulnerable and when she's emotionally vulnerable she tends to shut down. Which was Riley's big issue. So you've got someone with a fragile mindset talking to the one person who's always been brutally honest but supportive with her. He could havve talked her into anything at that point, but he was talking without all the facts. In fact I'd say from the moment Riley put his leaving or staying on Buffy it became a bad idea for her to go after him.