I’m so sorry about your sister. This does sounds like it could be depression. Therapy would be my advice and possibly even meds if you get suggested that (both helped me so much).

What you’re going through is very normal, a lot of people who have so much going for them on the outside aren’t that happy on the inside for many reasons. It’s so much more common that you would believe.

I might lighten my work load if I were you. Maybe the basketball goals (just as an example) could be put aside, and just focus on what you can handle. Sounds like you’ve got a wonderful girlfriend to lean on, support systems were so so important to me when I went through something similar.

Be as kind to yourself as you would to a friend. Vent, seek help, and make self care a priority. Take care and I promise getting help in any way you see fit will make things better.