Dear Diary , Trust and Forgiveness .... a myth?

Ever tried sustaining any type of relationship without trust, Its hard, trust me, its hard.Yes, i see the pun, and its intended,

This year, if i have learnt anything its how fragile and how important trust is, In any type of relationship, work, family, intimate?

I noticed that i have always been one to give people the benefit of the doubt, i trust implicitly at first sight and give people a chance to screw up before i start doubting, but then when you screw up even a tad bit, forgiving is almost impossible for me, i never ever forget, i don't know if its because i trusted so easily and i start to regret that decision, but a lot of the times i really cannot forgive.

Its such a bad trait that i'm trying to get rid off and so far, not having much luck, but i am trying, i especially find this problem in my relationship, i never forget anything, every fight or misunderstanding just takes a bite out of my feelings, makes me trust less and any progress i had made with trust goes right back to zero.

Its a struggle,not a comfortable one, trying to make things work and not making significant progress because you just cant forgive, or you just cant trust. Its one of the things i am determined to fix in the new year, the ability to let go, things really get to me a lot, baggage and issues from past relationships haunt my decisions and I'm always scared that i'm being taken for granted. That has to be the worst thing, that fear that I'm doing my best, but the other person feels entitled or does not appreciate it so i don't get the same courtesy back, even with my girlfriends its worse. 

The concept of being able to trust someone who already hurt you initially seems like a myth to me, after all they say we are supposed to learn from our experiences, is it not stupid, to know someone can hurt you without any thought and still forgive and trust them again, what is that saying about once bitten , twice shy?

But then, if you never forgive and trust, how then can you sustain any relationship because its a given that people will hurt you, and you will hurt people.

I'm still here, trying to wrap my head around it.