Ok, first you aren't to blame. But I am going to try to explain this mindset to you, as I understand it in my life, not to excuse it, but to help you understand why he may think this way and not actually be a bad guy.
I do not agree with this mindset, at all.
Ok, society as a whole victim blames. Victims of a previous trauma act some way to attract more trauma. If you didn't try to excape (in a kidnap and/or hostage situation) then you were a willing participate (one of my very struggles).
Even Bill O'Riley stated that Stolkholm wasn't real (speaking of the kidnapping of Shawn Hornbeck) stating that he was a willing participate of the sexual acts done against him to not have to go to school and based that on the fact he rode his bike down the street while kidnapped and didn't try to excape. It is why I will NOT have O'Riley even on my tv screen when I am home even if I am busy. Thank god I don't have to worry about that soon.
Anyway, society pretty much victim blames at every turn. Why didn't you tell? Why stay with him/go back to him? Why didn't you scream? Why did you hide it? Why did you do it without force? Etc. Society doesn't understand that victims do/don't do things for a reason. Threat, scared, shame, blaming yourself, etc.
Ok, so that's society alone. Then we get to how non-traumatize people think. They have no idea how we process things. How things affect us. They can't comprehend that we couldn't have stopped it or we had reasons to not tell (threat or even brainwashing). From how I am reading this, he is falling right in line with societal belief that if you had a previous trauma then you act or look some way that attract more victimizers. Or could have seen it coming some how and avoided it. Or not learning to defend yourself? Just a guess in that one.
Again, I don't agree with any of this but just explaining.
Also, he could be like my father. He is a *stick your head in the sand, don't want to hear about it, "no, don't you dare talk about it" and tell himself that it isn't so; or is so, and then it isn't or is so in his mind* kind of person. Say it isn't so and it isn't. So my childhood (a cult) is minimized to having a perfect childhood in his mind. He absoutly refuses to let himself believe it was even bad as if he did that then he would have to admit to himself that he missed massive flags, that he could have done something to stop what happened at 12 yrs old and on and he just cannot do that. So it is possible your boyfriend takes a lot of the blame about not seeing it and/or stopping it but in a way to make it ok in his mind, as a way to avoid dealing with it, he blames you as then he takes no responsiblity. Just a possibilty.
Young couples last all the time. I know 4 of them that have lasted from 14 - 16 to 35 - 40 and are very happily married with children and just have a wonderful life in general. One of them was my best friend in high school and her now husband is my 2nd cousin's best/closest friend since they were in diapers. If anything was being hidden i would have a much more likelyhood to find out. Nope, full respect on both sides, truely one soul together. 100% of themselves are still intact as they have boy's night and girl's night often. Hang out with individual friends often. So young couples can last. There is a much lesser chance to last but still very possible.
Indenpence can 100% learned while in a relationship. You are a couple and support each other and show the other love, but you are also individual people and must have individual time apart. Have friends seperate from the mutual friends That is healthy. It is also healthy for both to be involved with bill pay, income, spending. So that if one dies or (get a divorce) the other isn't completely lost and can be independant.
Not all is lost and you don't have to seperate/divorce as all this takes is education about assult, about PTSD, if you have a therapist let him sit in a few sessions with you and see if the therapist can help educate. Maybe even a couples counselor seperate from your therapist if your relationship isn't going well and even an indivudal counslor/therapist for him would be wonderful help because if he is taking blame for it but minimizing it as a way to avoid it then that can help him deal with it properly.
But, a bad guy, I don't think he is. I see no need to seperate but rather I see a huge oppurtunity to educate and offer him his own support (therapist/counselor). I do not agree with his stance but don't see him as a bad guy. Just an uneducated, likely avoiding his own shit, falling into societal view, guy.
Anyway, there's my 2 cents (or 4 cents).