In Charlotte Bronte's novel, Jane Eyre, why would Jane not stay with Mr. Rochester even if his wife is alive?

In Charlotte Brontë's novel, Jane
Eyre, Jane leaves Mr. Rochester, and she refuses to return, saying that
perhaps they will meet again one day in heaven.

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'One instant, Jane. Give one glance to my
horrible life when you are gone. All happiness will be torn away with you. What then is
left? For a wife I have but the maniac up stairs as well might you refer me to some
corpse in yonder churchyard. What shall I do, Jane? Where turn for a companion, and for
some hope?'

'Do as I do: trust in God and yourself. Believe
in heaven. Hope to meet again
there.'

Jane has nowhere to
go because she has no family, but is taken in at Moor House, where two sisters and their
brother St. John Rivers. Jane learns that they are all related, and that she has
inherited money from her uncle. St. John proposes; but then Jane hears Edward's voice
calling her one evening, on the wind, and she returns to
Thornfield.

Jane refuses to stay with Edward in the first
place even though she is in love with him because he is married already. Jane has very
strict morals and believes that to stay with Edward would be a sin because he has a wife
and is bound by the vows of marriage to her, even if she is
insane.

It is only after Thornfield is destroyed by fire,
and Bertha, Edward's wife, is killed in the fire (that she set), that Edward is no
longer bound by his marriage vows. At this point, Jane returns to Edward, even though
his home is destroyed and he is blind. Still in love with Edward, Jane agrees to marry
him.