Lied about virginity to boyfriend

My boyfriend just found out I wasn’t “really a virgin” and he lost his mind. I was SA when I was 8 by a relative. I hadn’t opened up about any of that to him, I’ve healed from it. I have peace now & don’t even think about that incident anymore (until now) He’s the first person I’ve ever given myself to, but he won’t believe me. What can I do about this? My therapist had told me it’s a social concept but that what was “taken” from me at that age doesn’t define anything.