This is kind of a guess, but I think Kristy never really loved anyone romantically. Her freedom and her work were very important to her. So when she heard that her sister (who was the family type) couldn't have children, she decided to find a good man and have his baby to give to her sister. That way she wouldn't have to feel guilty for leaving her sister alone all the time for work. Then when she had the accident she was scared of her sister having to face parenthood alone (maybe she was supporting them with money even). Or maybe she realized how unfair it was to not tell the father of his child. Either way I don't think she knew that she would die young nor did she want to share her lover (she just always wanted what was best for her sister and right for herself).
Woman can't share her lover/husband with any 1 even with her sister.n kristy refused to marry with her lover.just bcoz of her sis.how come she allready know that she will die at younge age.?