Along with everyone's input, I'd recommend the following:
First and foremost it’s about hard work and discipline. You also need a mindset. Everyone ahd good ideas and Thakkus made excellent points that are outside the box, but really important. It can take a while to get used to being hurt, and some people never get used to it.
From experience I would tell anyone to skip any traditional martial art and get into Kickboxing. Find a school that advocates shin kicks and western boxing techniques. Shin kicks have a lot more power than standard kicks and boxing is the most economical and powerful use of your hands.
A Muay Thai School would be good as well. Muay Thai seems well balanced, but a lot of schools don’t teach hand strikes that are as good as boxing. Hard hands are easier to master and more effective long term. There probably are Muay Thai schools now that combine their general style with western boxing. Kicks look good, but 90% of the time the hands knock someone out.
So in a nutshell for your striking game: I’d recommend shins and hands at a school that makes effective use of both. Also, learn to live with solid black and blue shins and constant pain for 6+ months and then enjoy it when they just don’t get hurt anymore. Make you friends feel sick when you are wearing shorts and kicking trees and fence posts with your shins for the hell of it. (Ummm...or like me you just want to show off...)
Without either of those I would take boxing.
If you can afford to go to 2 schools at once add a grappling style. I personally would learn as much as I could about Jiu Jitsu first. Of course, this is subject to availability. Wrestling of course is good as well. Being in an environment where you can combine all 3 is going to be hard, although there should be more and more schools coming over the next several years.
About Girls: They adjust to your schedule or they have to hit the road.
Her: “Honey, We’re going to this party/date/event…”
You: “Yeah, AFTER my training session…”
“But it’s my Daddy’s B-day Party, and important to me…”
“Yeah, well not as important as training. I’ll be there afterwards.”
Be a man and the master of your destiny. If a chick wants to come along for that ride she needs to support you. Chances are she’ll respect you a lot more for being a man anyway, even if chicks never admit it.
Trust me; Birthdays are every year, special events happen all the time. But you usually get one shot at the big time that is so easy to blow. You can blow it by skipping training once. You just lost mindset, and you may have missed a key experience. You lost conditioning. You forfeited discipline in favor of something else. Trust me, if you regularly put training before everything else, eventually people will understand. Or leave, in which case they needed to go anyway. But usually they will understand. Oh, and never think you know it all and can do without training.
Cold or Flu? Train that day anyway.
There is a lot more to this, but this is already a long post.