Good morning,
all people are different. You can't form an opinion about other people based on just one example. I'm not encouraging you to trust people "pretending to be a good friend", but don't think bad of them right away. Give them a chance.
To some extent I agree with you, but you need to understand what kind of things we're talking about, because it's easy to trust people in some unimportant matters, but when it comes to personal matters, you need to be especially careful. You are right, all people are different, but in spite of this, I would not share any frank information with anyone, which could be blackmailed or worse, used to harm me in the future