Why is he mad over something so little?

A guy I've been talking too for a few months and I were going great, until this past week.
This past Wednesday, the topic of sex came up. He is much more experienced than i am. I asked him if he would ever want a threesome and he said it was something he would consider, only if it's with another female. I am personally not into threesomes so I said so, and i said that's such a big turn off! He started repeating how my mind will change after i continuously said no. I got quiet, and he said okay he won't force me to do so and left the call. He didn't message me the next day. Yesterday he messaged asking if i had anything to say, and I said you were the one that got angry so you tell me. He read the message and ignored me.
Why is he so upset over something so small especially with my opinion? What should i do?
Why is he mad over something so little?
Add Opinion