You’re never going to get a virus from reading text that is sent to you on Facebook. The danger comes if someone shares a link and you click it; that link could go anywhere, including to a website that will attempt to download a virus onto your computer. It is good to hover over a link before clicking it and note whether the URL it says it’s going to (in Chrome and probably other browsers, this comes up on the bottom left when hovering over a link) is a trusted website.