I have problem trusting friends!

it happened when i was 10 years old. i made a new friend(a girl, lets call her "A"). we always hang around together and have common interest which makes me happy that we could talk about. During the same year we met, we were preparing for the upcoming exams and given approval to self study in our class. we sat together with our other friends and started revising. suddenly "A" gave a diary to me and told me to read it, so i did. she didn't say anything about the diary so i assume its hers since NO ONE will lend another person they don't trust their diary. before i can even let a word into my sight, another friend(lets call her "B") of mine walked to my direction. "B" snatched the diary and slapped me six times in the face. it doesn't hurt that much because "B" didn't put much force in it but i nearly cried when i saw "A" laughing quietly about two metres away from me despite i was being slap. my other friends saw the whole thing and helped me telling"B" its not my fault. that diary was "B's" and "A" did tell me about it. it was worst that "A" didn't even had"B's" approval to have it making me the culprit in "B's" account. i buried myself in the book and try to let the tears not flowing out. it pains me to think about it. why is it not "A" who should have helped me but my other friends. i stopped talking to her but not avoiding her since we still have school to attend to. i wished that she apologize to me the next day and then i can say: its ok since "B" didn't slap me that hard and laugh it off. but she didn't. she only apologize after 3 days since that incident. i can tell that she didn't felt guilty because i can saw my friends outside the classroom door peeking in at us looking worried. if its not because of my friend i doubt"A" will apologize. i don't wish to disappoint my friends so i put up with it. after some time i graduated and "A" moved away. i added her in fb knowing its her because i bet she forget about me. "A" talked to me as soon as i accepted the friends request. i still remember what she type: do you remember me. at that moment i want to type lots of nasty things to her but in the end i just typed a simple: "yes" thinking if she forget the incident or she never remember such a thing and making me looking like an id**t. then we talked a little about our life and ended the chat. i still hated her for it and always thought if only i have the courage to confront her and return the slaps to her.

i felt less confident in myself after that but it gets worse when "C" my another friend was friendly but avoid talking to me after holidays and left me in the cold. i can always fell the tenses in the air even if i start a topic for conversation she ended it with words. i start to reflex my action wondering if i said something wrong. even others start to notice the tension between us. when i finally confront her she said: nothing. i was very confuse but we still remain as friends but less interact like we used to. 

since then i was always afraid losing my friends or when they will betray me etc. i limit myself to those who know me well but i tried to break the ice several times since making friend is a must when you study abroad knowing no one.

can someone help me deal with my fear of betrayal of friends.