More, because I buy a different subset of books than what I normally read in e-book form at the library. (They have lots of general non-fiction and literary romance thrillers. I like sf/fantasy, historical/mystery, and particular specific non-fiction subjects).
Plus, the e-books I buy are generally available at reasonably low prices at pretty decent terms (yay for liking backlist sf/fantasy, often MultiFormat and DRM-free and cheap like not-too-pricey specialty potting soil, if not actual dirt).
I think I actually buy more books overall because of both print and e-catalogue library usage, both of which are fairly well stocked in my area.
Not having to pay to read books that only moderately interest me to begin with allows me to allocate my money to buying books I actually want, based on now having previously read them.
That's how I've gotten almost all my e-books: the title or author are something I'm familiar with and have enjoyed in the past (or came on very high recommendation from a trusted source and were available at a very low price, so I was willing to take a chance and splurge on one to try out.)
Long story short (too late!): using the library makes me buy more books, not fewer, both print and e-. They're just different books than what I overall get from the library (except for the ones that I decided were "keepers" that I wanted my own copy of).