Is it ok for fiance to hide her sexual assault blackmailer from a life partner, who is very loving, caring & understanding with emotional connection?

I got to find about her one year old sexual assault and blackmailer after thorough inspection of her phone.

She shared everything with me. We have mutual trust, love, care, understanding and deep emotional connection, but she never talked about him to me, who keeps in touch with her occasionally, but she never gave in to his demands.

Sexual assault & blackmailing doesn't bother me, but she hiding & defending him really bothered me. My trust is all shattered, but what is the best way to deal the situation?
Is it ok for fiance to hide her sexual assault blackmailer from a life partner, who is very loving, caring & understanding with emotional connection?
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