Is it possible for your computer to get hacked into through someone's router?

Is it possible for your computer to get hacked into if your computer is connected with another person's router? I'm in college right now, and my roommate brought his own router for our dorm. He had to put in his password so I could get connected to his router. Is it possible for him to hack into my computer and look at all my files and steal them? I have a 2 year subscription to Webroot SecureAnywhere to prevent this from happening, but I'm just curious if there is any dangers if your computers becomes connected to another person's router. I'm worried when I connect my external hard drives to my computer, he could potentially steal/erase my files from my external hard drives. I know this sounds crazy, but I'm a very crazy person.

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