Why haven't I been able to move on from the death of my mom, was I actually acting back when she died or was I really feeling lost and helpless?

Back in 2017, my mother died suddenly due to heart attack and since then i have not been able to move on from the incident. My life has gone south.. My academic performance plummeted drastically. And my mental health as well as my physical health has gone down severely. Back when she died, whenever I used to share my grief with any of my friends, they always behaved like either i am just acting or i am being overly dramatic. For instance, one time i shared with few of my friends about my struggles due to this, and one of them said that I am just acting and I am really not going through a tough situation. Another time when I shared the fact that how my life has been messed up after my mother's death to my girlfriend back then, she said that such things happen to everyone but not everyone keeps crying about it like i did... So i am wondering whether they were really right all along because even now after 8 years.. I don't see myself moved on from that incident at all. ( sorry for my bad English as it is not my first language)
Why haven't I been able to move on from the death of my mom, was I actually acting back when she died or was I really feeling lost and helpless?
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