WIBTA for continuing to date my boyfriend, knowing about my sibling's feelings for him?

I (21NB) and my sibling (19NB) had both been close friends with my boyfriend (19M) for close to a year and a half. I had known him for far longer (six years), but we weren't very close until we started talking again in early 2025.

My sibling and I were both good friends with him until they decided it would be best to leave the larger friend group about a month ago. At this point they were no longer really talking as often, and I thought that was the end of it.

A few days ago, bf decided to ask me out. Of course, since I had been harboring feelings for him for a little while, I said yes. Yesterday I came forward to my sibling about it while we were sharing a shift at our work. They didn't have much of a reaction and we continued working until lunch break.

When they sat down with me they confessed that they "had a crush on him," and was just surprised about the situation. I told them I was sorry, and unwisely said I always thought they were compatible. I know it was extremely insensitive and I regret it deeply. I have autism, so sometimes the realization doesn't immediately land.

Sibling and I continued work until they said they felt sick to their stomach. They've been unwell in the evenings recently, so I didn't think much of it at first. They left early, but I was left with a subtle nagging feeling that something was off.

Fast forward to this morning, and my little brother came to me saying that sibling bawled their eyes out to our parents and even passed out from sadness. Comes into light that they had tried going for him before. Apparently bf had told them he wasn't ready for dating for a while. I have no idea when this interaction happened, all I know is that sibling backed off when they were told this.

Obviously I can understand why it would be extremely upsetting to hear that the same guy who brushed you off went after your older sibling instead. I haven't talked to either my parents or sibling. I know I need to say something or apologize, and I'm working up the courage to do so. Confrontation is very difficult for me.

I feel absolutely sick to my stomach with guilt. I feel like an asshole. Bf only knows that I'm upset but not why. I really wasn't sure if I had any business telling him about sibling's reaction, even if it involves him in a way.

I don't want to let him go. I genuinely have come to love him so much over my time knowing him. That being said, I don't want to continue to hurt my sibling. Would I be the asshole?