You have to make time for some type of friend outside of your classmates, you know normal folks. They help to keep you grounded and give you a sense of perspective that is lost in the lab grind by the rest of us. For instance, I used to drink beer with the night janitor while getting my MS. When 11pm rolled around, I'd stop what I'd be doing and we would walk the halls drinking Bud Lights in koozies, bullshitting, and I'd help him empty the trash. I'd tell him about my problems, he'd tell me his, I'd explain my project to him, and he would ask me why I was doing something. I still miss our evening constitutionals, where we discussed life, science, why the PI down the hall was such a bitch, and whose turn it was to buy beer.
Moral of the Story: Make some damn time for friends. You are never going to have balance all the time in your graduate career. At some points you will feel like you are spending too much time in the lab or too much time on your personal life. That's fine, just let it balance out in the long run. How many scientists were there 200 years ago? A shit ton son! How many can we name? Not too many. Science is not your life, its something you are passionate about and do to live your life. Enjoy the people around you and let them enjoy you.
Now get your ass out of the lab and make friends. Oh and study too.