A married Christian woman wants to become Muslim and marry a Muslim man

Firstly:

We ask Allah to bless you and enable you
to enter His religion, and we hope that that will be in the near future.

Secondly:

If a woman becomes Muslim and her
husband does not become Muslim until her ‘iddah
(waiting period following divorce or separation) is over, then
it is her choice. If she wants she may marry someone else or if she wants she
may wait in the hope that he may become Muslim one day.

Ibn al-Qayyim (may Allah have mercy on him) said: What is
indicated by the ruling of the Prophet (blessings and peace of Allah be upon
him) is that the marriage contract is put on hold; if he becomes Muslim before
the end of her ‘iddah, then she is his wife, but once
her ‘iddah ends, she may marry whoever she wants, or
if she likes she may wait for him, and if he becomes Muslim then she is still
his wife, with no need for a new marriage contract.

End quote from Zaad
al-Ma‘aad fi Hadi Khayr al-‘Ibaad, 5/137

For more information please see the
answer to question no. 21690

Based on that, if you have become Muslim
and your ‘iddah has ended, and your husband has not
become Muslim, in this case it is permissible for you to marry a Muslim man and
it is not stipulated that you should get a divorce from the first husband,
because the marriage was annulled when you became Muslim.

Imam ash-Shaafa‘i
(may Allah have mercy on him) said: If one of the spouses became Muslim before
the other, and the husband had already consummated the marriage with the wife, it
is not permissible for the husband to have intercourse with the wife, and the
marriage is suspended until the end of the ‘iddah. If
the partner who had not yet become Muslim does become Muslim before the end of
the ‘iddah, then the marriage is still valid. But if
he does not become Muslim before the end of the ‘iddah,
then the marriage is ended, and it is an annulment without a divorce, and the
woman may marry whoever she wishes from that point.

End quote from al-Umm, 5/49

The length of the ‘iddah
in this case starts from the time when the wife became Muslim and it lasts for
three menstrual cycles if she menstruates, three months if she has passed
menopause, and until she gives birth if she is pregnant.

And Allah knows best.