In addition to the bars mentioned on this page you'll find most of the bars along the Alameda de Hércules (which is a popular hangout in Seville for having a beer and a chat) at least gay-friendly. And the gay bars there are also frequented by straight folks, so you'll often find a mixed, easy-going crowd. Just have a look and you'll easily find your favourite spots.
Important note: Due to the COVID-19 epidemic, many places are closed or opening hours may have changed.
Please check the websites and Facebook pages of the respective venues for the latest information.
Update 10 January 2021:
The night curfew in Andalusia is now from 22:00 to 06:00.
Bars and restaurants have to close at 18:00 at the latest.