My bf told me something I wasn’t ready for

I’m 27 weeks pregnant FTM and my boyfriend just told me he had had a threesome with his brother and a girl when he was in his 20s he’s now 34. I’m so emotional about it and in a bit of a shock as I didn’t know he was.. into stuff like that.. I feel so alone and trapped. I’d never think he was that sexual for a lack of a better term.

Upon saying it, he had tried to reducing it and saying he thought he had told me. I started crying and he’s saying I’m overreacting. I’m devastated. Not necessarily by the surprise but his response to me being upset.

Am I overreacting? It’s a hard image to get out of my head.. and it hurts tenfold that he deflects my emotions.