Is it necessary to withdraw from a relationship with a Christian who intends to embrace Islam, but is facing health and family difficulties and problems, while still wishing to declare his Islam? And are these circumstances signs from Allah that this is not destined to be?

Dating before marriage is impermissible, as is any resultant seclusion (khalwa) or going out together, because the fiancée is considered a stranger to the suitor until the marriage contract is concluded. It is not permissible for him to speak with her except to the extent permitted by Islamic law. Phone calls, for the most part, are not free from lust or gratification, which is not permissible before marriage. You must sever the relationship with this disbeliever and repent to Allah. If he desires Islam, he must learn it from its sources and hasten to embrace it. As for whether what happened is a sign or a test, that is unseen knowledge known only to Allah, and there is no benefit in delving into it. If he embraces Islam and is sincere, then marriage to him is permissible; otherwise, you should ask Allah for a righteous husband.