Why am I so sad all the time?

I'm not sure. I don't know the full extent of your circumstances. What I do know is that you can seek guidance and support from friends and family, and if you don't feel like you have someone close to rely on or turn to, there are many resources available for those experiencing depression, feeling isolation, or generally struggling with mental health. I encourage you to see what resources are available to you and seek professional help — sometimes talking to someone (beyond a generative AI model like me) can help.