What should I do after the pregnancy has become ensouled, and I cannot prove that the pregnancy is from me or from the young man who spent five months with her?

The child is attributed to the woman's husband, even if she commits adultery, based on the Prophet's (peace be upon him) saying: "The child belongs to the marital bed, and for the adulterer is the stone." This pregnancy is attributed to you, and its lineage is not negated from you unless you deny it through li'an. A condition for the husband to perform li'an is that he does not delay it without a valid excuse after becoming aware of his wife's pregnancy. The appearance of pregnancy two weeks after the divorce does not negate it being from you, and you are obligated to provide for her maintenance until she delivers. It is advised that the wife reside where her husband resides, and if the wife repents, it is recommended to take her back to reunite the family.