My boyfriend wants a threesome out of curiosity.

I don’t even know where to start. My world just completely crumbled in a blink of an eye. So basically, my bf asked me if I would ever agree to a threesome. I never thought that he was that kind of person so I figured that he was just asking me for my perspective. I told him no and I asked him if he wanted one—I thought that he was gonna say no since all throughout the course of our relationship, he seemed extremely genuine with me. He responded with a yes but says that he doesn’t want to do it purely out of wanting to have sex with someone but because he’s curious to see how it would pan out. I am in shock. I don’t know if I am overreacting or not but my heart aches. I can’t even imagine the thought of me being with someone else so this hurts me so much. I poured my heart out and I blocked him as of the moment since I don’t want to hear anything from him. Also, before I blocked him, he told me that I was acting crazy since he stated that he was loyal to me and that if he wanted to cheat, he would’ve already done it.

I don’t think this is what I deserve at all but keep in mind that I am also a sensitive person so sometimes I don’t know whether I’m being rational or not. I’m sorry if this is a difficult mindset.