Why is my guy friend cold towards me and nice to others?

So like my guy friend and I used to be super close, he told me everything he was doing, feeling and thinking during the day. I also helped him with his anxiety. But since over a year he became cold and distant. He takes a long time to respond, almost tells me nothing no more and his answers are short and unemotional. I did ask him what is going on, but never received an answer. The weird thing is, he is the complete opposite to others. He send me a screenshot of conversations he had with others a few times (because he needed my advice in something) and he was a completely different person there. Nice, talkative, interested, emotional, explaining in detail (while he only says what's necessary when talking to me) and so on. He also responds to them fast. What could be the reason, he turned cold on me?

Why is my guy friend cold towards me and nice to others?
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