Why do some women suddenly cut off male friends when they start dating someone new?

I've seen this happen more with women than with men. I know there are men who do it though. Thankfully, it's only happened a couple times in my own life. This seems fairly common because I've seen and heard a lot about it from women and other guys.

I'll have a female friend, typically platonic, where everything is going perfectly smoothly. Suddenly, one day she meets another guy and gets super cold and unpleasant with me. No explanation. No heads up. Just suddenly icing me out one day. Really mean, shitty, standoffish behavior. Shutting the door super hard, instead of just saying "hey dude, I've started seeing this guy and I want to focus on my connection with him. I'm not comfortable with continuing our communications, as long as he's in the picture."

Now, bear in mind that WE NEVER DATED. This is not someone I was romantically entangled with,

It would make a bit more sense to me if we were romantic. But to my knowledge, we weren't romantic.

So... what the hell? Lol Why do so many go nuclear on friendships when they start dating someone new?

Why do some women suddenly cut off male friends when they start dating someone new?
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