I really really want to train for a marathon, but I can't find anybody to do it with me, and I just can't seem to be able to train alone. At the beginning of the year I found someone to do these things with, and we did amazing things, from regular jogging to cycling to obstacle courses. But now he is busy with exams. How can I motivate myself to train alone? Or where can I find someone to train with?
Meetup is a useful place for meeting people with similar goals.
Most towns, especially college towns, have a local running club; surely you can Google around for more info. Or inquire at your local running store. They're usually very familiar with the local clubs and events.
The track club in my college town even led a marathon training program every summer. Perhaps you can find something like this. These are often very friendly to first timers. You can run with the group while making new friends to train with.
As someone who has been running for 12 years and has trained for distances from 13.1 all the way up to 100 mile races, I will say this about marathon training. You will fail if you rely too heavily on other people for motivation. You have to figure out why running a marathon is important to YOU, and let your actions match those values.
Running should be fun amid all the pain. If it's so miserable you can't do the occasional training run alone, something's wrong. Concentrate on what you like about it and don't give yourself time to picture the hard parts before you're out the door.