What is wrong with me? Someone please help!?

I have been in a relationship for 5 yrs. He has been wonderful for the most part. He has been the greatest daddy to my 9 yr old child that was denied by her bio. He treats me like platinum. He makes me feel beautiful, sexy, satisfying, and perfect. He puts me before his friends and family, we (my child and I) are his #1 priority. He does what he can to give us the best. He takes a lot of pride in us as "HIS" family. However, in the beginning as a single man he attended the strip clubs on occasion. After we had started developing a relationship and discussing our lives and interest, likes and dislikes, etc...He was like well I only ever went to the clubs for the atmosphere, i have never actually held any interest in the women themselves. I have no interest in going if you don't too. He had later asked me about a threesome or just me sleeping with another woman and letting him watch, I told him that I would never consider anything like that ever, but that if that was what he wanting or was looking for, he was free to move on to someone else, cause I was not the one for him. He was like no, no no can't blame me for asking. And he was right about that. I told him that I am one of these what most people today would call old fashioned, that I believe that if you truly love someone that their is NO-ONE else for you. You have no desire for any other, and if you do, you need to keep looking, and not settle. Now about 4 years into our relationship I found porn under my mattress, I had no idea. So I flipped majorly, I felt like I had been cheated on. I was very verbal and in depth about my feelings on this matter. We spent many days and nights talking, discussing and crying about this. He had a hard time seeing my point on the matter, he said it was just entertainment. I told him if it was just entertainment then why was it so important. In the end he said he was sorry for making me feel cheated on, undesirable, and so angry and hurt. He swore that it would never happen again, that he would not had thought I would react that way. Well then about 1 yr ago I had noticed that I had a lot of inappropriate material on my computer. So I started digging, and there was all these web pages and explicit searches. Once again I flipped, this time he denied it up one side and down the other. He tried to place the blame on my 18 year old son, easy to do. Well when I confronted my 18 yr old about this, he denied it as well. But when viewing the history, 90% of the days and times were not possible for my son to have done. So my man finally admitted it, apologized, and once again we were at a roadblock in our relationship. Now I didn't just worry about a cheater but a liar too. At this point I did not think I was going to overcome this one. And I did not overcome it undamaged, I lost a great deal of sexual interest and pleasure with him. It is still there just nothing like it was. Now just a couple days ago same thing, with the computer. I confronted him, he did not deny it. He sometimes has to go out of town and work. I asked him how could I trust him. He cheats on me in his mind. Why not physically as well? I told him he needs to decide what he wants, cause it doesn't sound like he wants me, or a family, or anything in particular. I told him as much as I wish I could hate him and make him leave, I can't. I Love him. I love our life, and I love our family, but I will not live with this.What do I do? I have 5 yrs. invested, i do love him. But I also have my daughter to think about, THIS IS HER DADDY!! The only one she has ever known and loved, and she is a major daddy's girl. And please don't get this twisted. I am extremely independent, I have never needed anyone to do for me financially nor otherwise. I have mostly always been on my own since I was 16, working going to school, paying my own bills, never depending on welfare, raising my kids by myself. So what is wrong with me, why can't I overcome this, or lose this feeling? I mean should all the good rule out the wrongness of this one thing.