A Secret Relationship 12 Years Apart

At a small green space, the protagonist — a self-deprecating 28-year old man who is on his way home — by chance meets a pretty high school girl who lives in the neighborhood. The two of them become drawn to each other after a number of encounters like this; but one night, the protagonist under the influence of alcohol lays a hand on her...!? (Source: DMM FANZA, translated)