OP, I am so sorry you were abused when you were younger.
And exploiting someone’s young age as a way to getting sex IS rape, it’s just a technique that is harder to identify while it’s happening. Grooming is designed to mess with your head.
You trusted your ‘boyfriend’ with something and he misused your trust.
You are not to blame for what happened.
And posters who ‘can’t believe you even need to ask..’ and similar may well be using a figure of speech to emphasise how much you are not to blame, but actually, it is exactly having had your head messed with that gives you those sorts of self doubt.
You are not wrong, or to blame for finding it hard to know where the rights and wrongs are: that’s how abuse affects you.
Counselling could be a good support for you.
Or you can contact Rape Crisis to talk this through. You don’t have to report it.
The talk in the news about the ‘grooming’ aka ‘rape’ gangs must be very triggering for you.
Your boyfriend is really really ignorant and steeped in the misogynistic view of blame culture. And not on your side: how could he listen to you tell him something that you were upset and vulnerable about and blame you? Not a safe person.
You did a good thing coming on here to get support and perspective, well done for looking after yourself.
And again: so sorry you were abused.