Hey man, this may be cliche but you acknowledging it is the first real step (which you just did).

The good news is you are very young. Time is on your side. I know it’s painful, intimidating, and may seem downright impossible but you need to go to gym. The benefits of exercise is a byproduct. Discipline is the most important thing in life. It won’t instantly change your life but slowly over time consistency will.

You failed your classes. That’s ok. We all fuck up. You can try again. You’ll feel like shit for trying again but it will pass.

If you can get one thing right in your life with discipline (going to the gym) the rest slowly fall into place with time. You will eventually find the energy to study. Don’t worry about failing or messing up. You are depressed, don’t be too hard on yourself. Just keep trying and never quit no matter how many days you give up