I think it did cross her mind to marry him, as it seemed she might have been having second thoughts about not having marriage and children. I think she might have been more attracted to him than to some others, because she met him in person, whereas the others were known only portraits and reports. But, she must have thought she was crazy to think that, because it would have been very bad judgement. She didn't so much keep him dangling because she wanted to, but because she could not make up her mind. In the end, time sort of made the choice for her. But, indeed Leicester was most likely the only man she ever seriously wanted to marry, not that I believe she ever considered it.