Luddite Question about my iPod

Okay. I'm so dumb when it comes to tech stuff.

My hubby used my laptop to download some stuff on HIS iPod, and now all his music is on MY iTunes library.

I tried just un-checking his music, but it still all appears when I synch. I went though and left clicked and DELETED all his music, and yet. ... THERE IT IS AGAIN! Both in the library and on my iPod.

HOW DO I FIX THIS SHIT?

Thanks in advance!