My fiance molested my daughter, what should I do?

My name is Rita I have a wonderful daughter and a fiancee that we’ve agreed to get married by the end of the year, though he was not the father of my daughter, I had her when I was in school, though her dad is late now. when I met my fiancee he agreed to take her in as his own daughter when we finally marry.I love this my fiancee, that I can do anything to be with him and I know he loves me so much too, even his family do same, but then one day something happened,I came home and my daughter ask me what is the meaning of Virgina and I ask her who was teaching her all this?? she said her uncle, when my fiancee came I then ask him what he was doing to the extent of teaching my baby such,he laughed over it,then it started ringing in my mind that I should be very careful on how I leave both of them together, one day I came home and found my daughter crying in her room when I went in there I ask her what and why the cry she opened her legs to me and I was very surprised that I nearly fainted if not that I came home with my girlfriend.There was blood everywhere,and bruises,that I taught armed-robbers came to my house, when I summoned courage to ask, she said uncle pushed her to bed when she came out of bathroom and had his way on her. I was really mad and shouting that neighbours rushed into my house to find out if someone died but when they got in they were all in tears after what they saw. They ask me to call police at once.I tried my fiance’s line but it was switched off.It was not that I am not living with my fiance, he comes and goes.Please my dear friends what do I do??because I am in total agony and pain, and I’ve lost so much in crying and being here and there out and in hospital to make sure my daughter is sound both in health, emotionally and psychologically.Just two days ago my so called fiance came to my house with his elder brother to ask for my forgiveness I just called the police at once to come and arrest him but his elder brother said I should not do that, let settle in peace.
Now wht do i do?? to forgive or still insist for his arrest??
what do I know will happen in future if I continue with the marriage my daughter will always be in fear and trauma
Please your advice is highly needed.
Thanks Rita.