It seems to me, admittedly based on very little info, that you might have fallen into a pattern/vicious cycle of expecting the worst in people and consciously, or more likely sub-consciously, doing/saying things that brings about the worst in them before they even have a chance to be nice/not betray you(I used to do this very thing sub-consciously when I was younger).

Try as much as you can to make sure you are not doing/saying things that cause your expectations of other people being horrible/two-faced to be a self-fulfilling cycle. Making sure you are giving people that you meet a "fair shot" is vital so when that rare-ish event does occur and you do come across a genuinely nice/caring person that you do not miss out on connecting with said person due to the trauma others from your past have inflicted upon you.

Anyway, when I was younger(HS & College age... I am 32 now :(... So damn old! * sads * ) I had a complicated family-life for which I believe, in retrospect, led me to find the wrong type of friends for a spell who were at wayyy too young of an age to use drugs and drink in the manner in which we used them(AKA: In a way that is very self-destructive). Anyway, my point being to simply try and avoid hanging out with other people your age who have substance abuse issues. As no matter how much a person who is using substances in a reckless manner cares about you/likes you they WILL be 1,000,000x more likely to "betray you" than another person who does not have that shit in their life. So make sure you are looking for the right group of people to find friends from as the odds of them being "two-faced" increases exponentially when they have substance issues.

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TL;DR - REALLY SORRY THIS POST GOT AWAY FROM ME! Read below:

I apologize for this post turning into an epic sized novel. I just wanted to let you know there truly are multitudes of people out there who have been where you seem to be. Also, I PROMISE that if you start looking in the right places you are much, much, much more likely to find others who are not prone to stabbing those around them in the back ;). Feel free to PM/DM me if you want. Good luck!

-Ben