Your login details are stored by your browser (Internet Explorer, Edge, Firefox, Chrome, Safari or whatever) so that you can access AB straight away. However if you've configured your browser not to store login details, or if you delete its cookies, you'll need to log in whenever you visit AB.
So it's something which you need to sort out at your end, Danny, and nothing to do with AB itself. Let us know which browser you're using and what type of device you're using (PC, Android phone/tablet, iPad, etc) if you need further advice.