I just started law school & took some classes over the summer to lighten my load a bit. I did alright and ended up in the top half of my class while managing to run 85 to 115 miles a week. I think you can do it. However, I'm honestly not that concerned about getting amazing grades in law school as I did in my undergrad. I have some good connections and have a job lined up if necessary post law school that will pay the bills. A lot of people say it's a huge deal to get great grades in law school, make law review- but I'm okay with being average & happy. I only put in about 50-70 hours of work a week and seem to enjoy the process & what I am learning more than most others around me.
My running has been okay, but nothing spectacular. I am currently running on the team since I got my undergrad & it's been quite a bit of fun. It's a total social thing & gets me away from some dbags in the law school that are incredibly full of themselves. I'm still relatively competitive & can kind of contribute to the team. (although my 5k PR isn't 13:30 like most letsrunners)
I don't really party too hard on the weekends although, a beer or two here and there isn't a big deal. I have a girlfriend, but it's not serious. I just think if you manage your time well & be mentally tough. You can run and be successful in law school. It's tough, but it's totally manageable. Most people I know that are successful in my class work out everyday or are alcoholics. You need a stress relief. It might be hard to do workouts, but if you get out the door for just a bit you will feel much better.
Good luck OP & yes, you if go to law school, chances are you are probably a tool or some sort of an asshole. I can admit it.
Also, yes, becoming a lawyer is a terrible occupational choice, but just because you go to law school doesn't mean you have to become a lawyer... A law degree opens up a lot of windows professionally.