Why is my family telling me to move on and let go of my mother (brutally honest answers please)?

I overheard my dad talking to my oldest cousin about me dwelling on the last. He was like, "She needs to let go. Her mother is dead. Gone. Finished. She gets angry and jealous when she sees people bonding with THEIR mothers and she needs to stop the jealously. I know it's normal to feel that way but she should be happy they have their moms still snf she should be happy of the wonderful years she had with hers. I told her, 'Look I know you miss your mom, but she is gone. She isn't coming back and once people are dead. They're dead. Once they go to heaven, they won't wanna come back to this cruel world. Stop dwelling over the past and you need to focus on yourself and move over and take care of yourself. Put your big girl pants and be a WOMAN.' She should know she isn't coming back. She always drags people down when they're trying to be happy and she gets upset that they are happy and she is still angry about four years ago. We all are still but we all moved on and that's what she needs to do. Let go of her mom.'"
I looked at my dad and he was like, "Yes, I'm taking about you missy. You need to move on and stop living in the last." My cousin said, "Yep that's true. That's the truth."
Even my friends are telling me to move on and when they have fun at an event, when I bring it up, my bestie cuts me off anc said, "We're not discussing that tonight. We're having fun and they're no sense of being sad."
I told her I know but I can't help and people act happy and never happened and don't care that I'm said. My best friend got irritated saying, "Look! It's a party and we're supposed to have fun, not drag people down on your misery. Maybe someome should break outta YOUR misery. You mom would knock some sense into you right? SO can't be sad all the time. Your mom would want to have fun but instead you keep trying to drag everyone down! It's going to ruin your life. Smile! Have fun. We're not doing this tonight. If you're going to keep doing that and talk about your mom, I think you should leave." Then she walked off. I can't believe my best friend said that to me. Can you? Sorry of this is long to read.