Why is it hard for someone to forget something bad that others did to you?

[starpreneur009]

I specifically want a GIRL'S POINT OF VIEW on this one
is it hard for you to forget something bad that others did? How long does it take for you to forget? And may pinipili ba kayong taong kakalimutan ang kasalanan?
NO LOVE INVOLVE LIKE IN BF/GF OR HUSBAND/WIFE or CRUSHES

I had this friend and classmate kasi (Let's name her Girl A) I said something hurtful to her and nagalit siya sa akin
but I said sorry, sincerely (i'm not joking here I really said it sincerely), sabi naman niya naforgive na niya ako, pero medyo hindi pa rin niya ako kinakausap ng maayos,
naisip ko hindi ko muna siya kausapin, para magpalamig ng ulo niya and may awkwardness din kasi eh
tsaka hindi rin kami nagkita for two months because of summer vacation from school

so after ng summer vacation plus after two months of school
ganun pa rin siya, hindi pa rin niya ako kinakausap ng maayos and like dala-dala pa rin niya yung sama ng loob sa akin

yung isang guy palagi namang inaasar si Girl A and one time naiyak na si Girl A sa sinabi niya and there are many times na nagalit na rin siya sa guy pero naguusap pa rin sila after parang walang nangyari, pero pagdating sa akin iba siya