Why are guys so hot and cold?

I have been friends with benefits with this guy for about 6 months. We are #1 BFFS on snapchat and we talk every day. Before he was very sweet and respectful. We would play video games online when we weren't together, and we even joked about taking a trip together. He would straight up act like my boyfriend without the title. Then I called him out on some disrespectful behavior, and he has been distant ever since. It's like he couldn't handle being called out for acting rudely.

We used to have such good communication and now the relationship feels super distant and cold. We have always agreed that we were single and this was a casual relationship, but it's confusing to me why he went from acting like a boyfriend to being cold and telling me that he is hooking up with other people. Up until a couple of weeks ago, he wasn't looking to hook up with other people besides me. Now he is very obviously seeking out other relationships.

Why do guys act so sweet and then all of a sudden switch to being cold. I thought we were cool but now I'm just disappointed in the way he is acting.
Why are guys so hot and cold?
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