Either you have some kind of system backup software running or your roommate is reinstalling it. foobar2000 is a well behaved piece of software, it won't exhibit any kind of nasty installation tactics like you describe. However if you downloaded an installer from an unofficial website there's no telling what else might be bundled along with it - perhaps some adware that is part of the install is "repairing" foobar2000. If you still have problems, try the official foobar2000 forum at
http://www.hydrogenaudio.org/