Though he’s newly split, Ben Affleck wasn’t solo on Thanksgiving: He celebrated the holiday with his ex-wife Jennifer Garner and their three children, Violet, 19, Seraphina, 15, and Samuel, 12. Affleck—whose wife of two years, Jennifer Lopez, filed for divorce in August—spent the first part of the day at the Midnight Mission’s annual street fair in Los Angeles, where he and Garner, both 52, and their kids served meals to the city’s homeless community. “The kids love having everyone together,” says a source. Afterward they all had dinner at Garner’s home. Having her loved ones under one roof buoyed the actress, who has been “heartbroken” over the recent loss of her beloved golden retriever Birdie, says a Garner source. With Violet, a first-year student at Yale, home for the holiday,…