There was a manga where a girl kisses a younger girl and stuff when they are both very young. She later comes to regret it because she thinks she took advantage of the younger girl (or something like that). Either she or the younger girl moves away, however, they eventually reunite later on and the younger girl initiates the kissing and stuff. I’m pretty sure it was NSFW. It was probably Age Gap as well. Sorry if this description isn’t the best.