I probably won't be exaggerating if I said I had one of the worst experiences in grad school, not academically, but mostly dealing with personal issues and such... I struggled a lot to the extent that I had to see a psychiatrist and a therapist later in my PhD. With all that, my advice is
Stick with it, you will be done, and you will be great. It will ruin your self-esteem, but with all that, trust me you are still great. Years after my PhD my boss still tells me I am doing a great job and I learn incredibly fast and all I can think of is how incompetent I am (lookup Impostor Syndrome)... it's unbelievable how much grad school fucks up your self-esteem.
Exercise, exercise, exercise. Did I mention exercise? Don't let it go, don't ignore your body. I really cannot stress just how important this is. Start running or hit the gym. Join a club if you find it hard to exercise alone. Eat well. Take care of yourself. This will give you a sense of control over yourself, you will feel that grad school is just a part of your life. It's an important step, but it's not all you got.
Have hobbies. Try photography, read books... something. The benefit you get from this is that grad school doesn't become EVERYTHING you have. It's just a part of your life.
To manage all of the above, you need to be organized. Get into a routine, get up early, go to work. When you work, you really work. No distractions, give it 100% of your attention. I remember back in grad school I installed some extension in my browser to block reddit, etc. Look it up and do it... It works. Leave work at a specified hour and do not work at home (unless of course you have a deadline, etc.). I assure you if you were to work efficiently from 8 to 5 everyday there won't be a need to work late nights. I find organization is key to having a balanced life with so much workload.
Ignore the worries for now, thinking of how the future is going to be, or what are you going to do with your degree... keep it in mind of course, but focus on what you have now at your hands and try to get the most out of it. Life will take care of the rest. Trust me, it will work out.