I'm in the same boat as you are, but I want to let you know that the friendships that do turn out to be fake or based only in obligation are not your fault. You, like every other living being, crave and deserve attention and affection. There will be people who are happy to give you that, and there will be people who give you that out of selfishness or other means, but you are not the cause of whatever they end up doing. No one person is ever the entire reason for a fallout unless they are abusive or cut someone off completely without discussing it.

Someone didn't really click with you but they didn't want to hurt your feelings by saying so? There might have been problems on your side and theirs that can't usually be solved in new relationships anyway, so it's nothing to feel guilty about. Hopefully in the future the other party will pick up on the fact that you'd rather be told the honest truth than be lead on.

A girl snapped at you for being clingy when she was the one fostering the relationship? She is absolutely the one at fault there. She had the choice to not pretend like she liked you, to leave sooner, to not insult you and make herself out to be the victim. You were nice, you wanted to be her friend, and unless you did anything truly invasive or aggressive there was no good reason for her to make you feel bad.

You can't be at fault for not noticing "signs." Some people don't clearly show or tell how they feel, and some people don't pick up on how others feel, but since it isn't controllable you cannot be blamed for it.

Think about it this way- say someone buys you a new car that is a model you've never seen before and they take away all other methods of transportation you have. The symbols on the dash are unfamiliar, so you don't know when to change the oil or something like that. Is it your fault for not having googled this random vehicle on a whim in the past, or is it their fault for not explaining the car they gave you?

If the people you want to be friends with don't communicate well, it isn't your fault if things don't work out, though you have to be careful about backing away without warning. It is admirable and maybe advisable that you brush up on body language and hints and all that, but along with that, you might have to ask outright how people feel. If they say they do like you but later turn out to be lying, you would not have been the problem because you did your part in the relationship as best you could and at least tried to talk about it.