This is a modern Coffee Shop AU where the Elderbrain happened, but Astarion was never part of Tav's group. The event was about 5 years ago (or more or less, depending on what the story-timeline demands) and Baldur's Gate has moved on, so to speak. So have the characters.
So with everyone leading his best life, Astarion barges in, and suddenly, people who had drifted apart come together again.
Wyll wants to make his father proud. Shadowheart has her hands full with the House of Healing. Lae'zel doesn't get it but trusts Tav ... kind of. Karlach is mostly around because she needs coffee! Halsin barges in because his lover calls. Gale ... well, you don't leave your ex to struggle on his own.
And Tav? He just wants to make coffee, not deal with rude customers and pay his bills on time. Is that really too much to ask?