The best way to share your library with a spouse is to buy a second Kobo reader and register it to the same account. You can read your library on yours and he/she can read it on their own Kobo eReader. The only drawback is that when you begin reading a book he/she already read, your Kobo will offer to sync to the "last page" you read, which is the last one your SO read. Easy to solve by archiving books when you finish reading, and then downloading archived books when your are ready to read it too.
Actually, you can get Kobo to delete books from your eReader. Login to Kobo.com, go to your library. If you have one of those OMG! what was I thinking
moments, you can delete the book from your library on this page. Kobo will ask if you're sure. Say yes. But it nags with warnings that the book will be gone for good. You have to hit the "Yes dammit" button, then the next time you sync: <poof>