I'm sad that my long distance girlfriend is having fun with her fam during new years, and I'm stuck at home.
Why are you sad about your girlfriend being with her family?
Because I can't be with them and have to be by myself.
Instead of focusing on what you don't have, you should try to see the bright side of your girlfriend having a good time. She can tell you all about it when she gets back and bring that joy into your life.
It's not like I'm not having fun here, but I just know I'm missing out on a good time with them.
Like you said, you're having fun where you are now. So, you should be grateful for that and focus on the good times you're having right now! Then, when you see your girlfriend again, you can both exchange stories of all the fun you had and relive the moments together.