He's totally interested in you. Coming from a guy, his actions would mirror myself if there was someone I liked. I bet he hung around outside the library before closing, fighting with himself to go in or not.
Want to be a little more aggressive? Next time he checks out a book, do your usual routine but write out your number on another sheet of paper and tuck it into the book before you hand it to him, in plain sight so he sees it. Then say: "In case you want anymore help, give me a call" then smile.
That should be his green light and he'll follow up.