Gender-Sexuality Alliances (GSAs) are school clubs for LGBTQ+ youth and peer allies to support one another. This eight-week weekly diary study considered whether a youth's positive and negative affect during a given week could be predicted by experiences in their most recently attended GSA meeting. Ninety-nine GSA members (M[subscript age] = 15.90, SD = 1.33; 79% LGBQ+; 41% trans/non-binary; 59% youth of color) in 11 states completed weekly surveys between January and May 2021. On average, some youth reported higher positive and negative affect than others. Youth also varied notably in their own positive and negative affect from week to week. Youth reported relatively higher positive affect on days following GSA meetings where they were more engaged than in other meetings and had spent time socializing in the meeting. Youth reported relatively higher negative affect on days following GSA meetings where they had discussed personal concerns, and relatively lower negative affect on days following meetings where they were more engaged and perceived greater advisor responsiveness. These findings offer a dynamic portrayal of youth's varied experiences across GSA meetings and the more immediate predictive effects of GSA experiences.