What does it mean, when a guy stops talking to you after you mention another guy?

So, I’ve been friends with this guy for about 3 years mainly on social media cause we live far away but we have met twice.

We talk almost every day, we are just friends though nothing more and he knows that.
A few months ago I told him I was talking to a guy and he was all good with it.

Today I told him I was talking to a guy and he ignored me, left me on seen and completely stopped talking to me. So I messaged him again and asked what’s wrong then he didn’t message back.

He has never done this before no matter how busy he is (I know he wasn’t busy because he was still online) It’s just weird that he is like this all of a sudden. Is it because he’s scared I’ll stop talking to him? Is it because he is jealous?
I really don’t know what to think.

What does it mean, when a guy stops talking to you after you mention another guy?
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