Is a fiancée permitted to lie to her fiancé about her previous relationship with another person, and is the fiancé obligated to forgive her for her past relationship and for giving conflicting answers?

Do not seek to uncover your wife's hidden past, for "one who repents from sin is like one who has no sin." Do not follow the suspicions and doubts stirred by Satan. Have a good opinion of her, look at her present, and let go of the past. Strive to deepen faith between you and build mutual trust. Beware of fueling suspicion and doubt, for the Prophet, peace and blessings be upon him, said: "If you pursue the faults of people, you will corrupt them or almost corrupt them." There is no need for you to uncover an old truth that might lead to wronging your wife after she has reformed her ways. Turn away from thoughts that push you to pursue misdeeds.