Forgiveness- My personal input

Forgiveness- this is a huge word for me.
I find it very hard to forgive someone so easily, specially when it's someone I love very much, thought they loved me very much or I guess it had to do something with expectations.
There are all these sayings about forgiveness and a friend of mine said to me, "honey, forgiveness is the greatest thing you can ask for and the greatest thing you can give."
Forgiveness, according to Webster Dictionary is, "the act of excusing a mistake or offense"

for⋅give 

verb, -gave, -giv⋅en, -giv⋅ing. –verb (used with object)

1.	to grant pardon for or remission of (an offense, debt, etc.); absolve.

2.	to give up all claim on account of; remit (a debt, obligation, etc.).

3.	to grant pardon to (a person).

4.	to cease to feel resentment against: to forgive one's enemies.

5.	to cancel an indebtedness or liability of: to forgive the interest owed on a loan.

–verb (used without object)

6.	to pardon an offense or an offender.

I think the biggest reason people are not able to forgive is because of trust. Trust plays a large role in this because how do you that someone will not do the same thing again and ask for forgiveness.
I think the same has to do with sorry. My roommate explained, "Sorry is a crazy thing. Some people will meaningfully and with all their heart say sorry, and others will say sorry in a manner that, "I'm saying sorry, but I will repeat the same mistake and say sorry again, just like this"
I tend to apologize a lot for things I don't need to say sorry for.
Back to forgiveness. I find it very difficult to fully let someone off the hook. I may not mention it in relationship, or between exchange of conversation, but I will always have a note in my mind about the "offense or mistake"
Also, there are mistakes/offenses that are worth forgiveness, and how does someone measure that. Whether or not something should be forgiven. I guess it depends on each person.
Sometimes I think I should really with all my heart forgive someone, it would be very high and mighty of me and will really affect my happiness or content level.
Other times I think, I am not god. I am a human being and I don't need to forget when someone has hurt me... Which brings me to a new dilemma... Forget vs. Forgiveness.
Again, how do you define the two and draw a line. There are things I have forgotten, but will never forgive. But there isn't anything I have forgiven and forgot. If I have forgiven something, I definitely have not forgotten it. So this means I really haven't forgiven it?
(This is an example of arguing in a circle)
Back to my first claim, I have a hard time forgiving someone specially I love them very much, or thought they loved me very much or expected a lot from them.
If someone loves you so much then they should have hurt you and question of forgiveness wouldn't have arose.
But if you love someone so much then you should be able to forgive them.
Forgiveness is a big and tough puzzle for me.
Another phrase that plays a large role in this is "holding a grudge"
Apparently, its a bad thing to hold a grudge, but how do you forgive someone who has hurt you so much... and its not a bad thing to say to someone that I can't forgive you, but its bad to hold a grudge, which is assumed as the same thing as I can't forgive you.
Quotes that confuse this even more:
"I've learned that people will forget what you said, people will forget what you did, but people will never forget how you made them feel."
"If someone hurts you, betrays you or breaks your heart- forgive them. For they have helped you learn about trust and importance of being cautious to who you open your heart to."
Maybe someday I will be able to forgive someone who has hurt me to a point of numbness with all my heart. I don't know when that day will be.
Right now I do know that there are some people I have forgiven cause I know they truly deserve it, they have paid the price and their eyes, actions and words tell me that it won't happen again.
But there are some people that its close to or impossible to forgive because they have repeated the mistakes, have a very weak sign of remorse and don't deserve it.
Sadly there are people that I have put my every drop of blood and sweat into are in this world that will be impossible for forgiveness.
And of course someone else who wouldn't be forgiven as per society morals.
To be very clear with my self, I have made a mistake that is not worthy of forgiveness.
My questions of forgiveness vary and will be very difficult to find answers, but I have to accept the facts and try to find peace in this.