What am i meant to do? Do i finish with her?

I'm 15 years old and I'm still going to school. I live with my dad who is Police officer in (CID). My mum died when i was only 3. I'm going out with a girl who I really like. Shes really pretty. We have been wanting to have for a while but we have never really got round to it or done it as she doesn't want to rush things. Just last week, we decided we would go for it. So we wanted to do it somewhere where no-one is around. I said we couldn't do it in my house as my dads always around. He works in CID, but he is always coming in and out of the house. She also lives with her mum and dad.I asked her if she had any ideas of where we could have privacy and she said I could come round to her house and her mum and dad will be out. So thats what i done. On the night i went to her house about 8 o'clock so that we could have till about 10pm together as her mum and dad wouldn't be back about 11(pm). But after about 20 minutes we were both naked and were doing it. We heard the front door go and before I could hide anywhere her dad caught me and her naked. Her mum wasn't there though. It was only her dad. He through me out the house and told me he will kill me if i come anywhere near his daughter. He then through me out the house naked and then he through my clothes out. As i bent down to pick up my clothes he kicked my backside. It was really sore. If it wasn't for his daughter shouting at him and telling him to stop getting so aggressive i dont know what he would have done to me. i then saw my dad's car after i had put my clothes on round the side of one of the neighbours back garden. Someone had obviously phoned him. I then walked out towards his car. He started shouting and saying is it true what you've been up to and your only 15. He said I didn't bring you up to carry on like this. He just kept on shouting and then he said wait till you get home. I had never seen him this angry before. He then pulled the back of my jumper and dragged me into the back of the car and drove me home. When i got home he told me i was to go to my room and i was grounded. I have only been grounded 4 times in my life and he has never been this angry before. I asked him why and i told him that we used protection and he just said do you think that makes it okay. I then went to my room. After being in my room 10 minutes I then walked out and said I'm going to see my girlfriend. We have got a right to do what we like. He said if you dare leave this house i will. Next thing I new i was back in my bed room. I was handcuffed to the bed. He has never used handcuffs on me before in my life. I was lying on the bed a long time, all i could think about was is this what he does to people everyday when he goes to his work. He came into my bedroom and i begged him to uncuff me, but he didn't say anything, he just took my Laptop,tv,ps3,computer games and everything out of my room. He then went into my pocket as i was lying on the bed and took my phone out. After another about three hours my grandfather came into my bedroom. My grandfather lives about a good hour drive away from where we live so my dad obviously contacted him. He came into my bedroom and sat down on a chair next to me. I asked him to take the cuffs off of me. He started going on about how i can't go around doing what i want and how I've to respect adults. He then says that my dads been to soft on me and letting me get away with to much. He said to me do you know whats going to happen now. I asked him what he was talking about. He said to me when i was your age and if i had done what you have done i would have had my pants down and got the belt. I've told your dad to give you the belt when you were younger, but he was to soft on you. Then he said i've told your dad to give you it now. I told him that i was told old and that he can't use his belt. But my granddad didn't listen. My dad then came into the room and said to me that he was going to take the cuffs off and he told me that i was going to bend over the chair in my bedroom. I said that i would do it. He took the handcuffs off and then i ran for it, my dad then caught me and he had my arms in a position where i could move. He puled me back to the bed. He put the cuffs on me and he said why did you have to be smart. My face was in my pillows and he had the handcuffs on me really tight. I started saying to him i will report you and you will loose you job. He just said you do what you like, just remember i'm a police officer and i'm your dad. I couldn't believe what he was doing. He then loosened my trousers and he then pulled my boxers off. He started saying you going to respect me from now on and your not going to be doing what you want. He hit me with his belt about 20 times and hit me with the buckle about 5 times. My backside was killing me and i was really upset. I looked in the mirror and my backside was all bruised. I was bright red and it had some black and blue marks on it. My grandfather had left by now. My father took th