Reasons for an ex-boyfriend to hide his new relationship?

There of course can be several reasons. But I am still curious as to why some ex boyfriends do?

And when I mean hide, I mean hide it on Facebook, in person, everywhere. If the man is no longer in love with his ex, why would he be so secretive about the new relationship if in reality he is doing nothing wrong?

For example:

I have a friend that went through a very terrible break up. About 4 weeks after the break up, her ex started hanging out with a girl he just met. Within the month, they were dating. However, my friend did not know because he hid it on his Facebook and even from some of his close friends. I only realized it because the girl he began dating was doing the whole "look at me look at me, I got a boyfriend" routine and making sure it was obvious on her Facebook. I deleted her after that. I have yet to tell my friend that her ex she still loves (who is ignoring her completely) is hiding his new girlfriend from her sight. He even blocked my friend on Facebook too.

I am not a fan of the guy, he was hurtful and cruel to my friend and I would of expected him to go out of his way to rub it in her face to make her feel worse because that is the kind of guy he is. This took me by shock to watch him actually HIDE the girl...

So as asked before, what are some reasons for a man that left his girlfriend and ignored her hide a new lover?
Reasons for an ex-boyfriend to hide his new relationship?
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