You sound like a sweet sensitive person who's been hurt way too many times. It does hurt to be let down, snapped at, and to be stuck around catty, vindictive, backstabbing behavior. In fact, too much of that is infuriating and inducing of hate and outrage.

With too many repetitions, sooner or later, one might come to expect the same bad experience to keep happening over and over, and fail to keep an open mind and fresh perspective for each new scenario and person. Emotionally speaking, when someone's been hurt or wronged, sometimes the slightest hint or reminder of that past event (by another person) will set off powerful emotions. Personal feelings are NOT necessarily caused by someone around you. Sometimes emotions surface due to reminders of the past that are ever so subtle, yet powerful. When another person seems like a complete jerk, take a break. Reflect on the situation. Separate emotion from fact. Ask yourself if that person's intentions were really as bad as they seemed? More importantly, what caused the emotion? Could it be an emotional response primarily brought on by something from the past? Nurture yourself. Love yourself. Work to process events in the past that continue to haunt you and ruin current relationships. Consider keeping a diary of bad emotions and a list of potential causes, including actual events, people, stuff from the past/reminders, and health issues (like a poor diet). Knowing yourself is the best thing you can do for yourself and others. Once you understand yourself, life will become much more enjoyable.

Giving people the benefit of the doubt is a fine thing to do most of the time. If you are ever worried about having that mistaken as foolishness, you can always verbalize it. It is good that you realize that, "people are not perfect and mess up again and again." Everyone comes with imperfections. People are not black and white, good or evil. We are all a shade of gray.