If you are both using the same computer. Then ideally, you could set the iTunes folder to be used by both of you as a shared folder as suggested above. You will have different lists of songs however. But exported playlists would then work. And/or also, he could add all songs from library to the library so they are added to his list. I've done that on my computer between accounts. Several accounts on this computer.

(iTunes creates a separate library.dat file for each user account. So even if the songs are in the library, one account won't see another user's songs in iTunes unless manually added via dropping the files/folders onto the iTunes library icon. Or alternatively swapping playlists between accounts.) Sorry if that all sounds confusing. At least this is how it used to work. I just verified, one account does not see what another account has added to iTunes even if using same location for iTunes library unless my suggestions are used.