So the guy i like (that likes me back) did this what should i think?

so the gy i realy like told my freind he madeout with his sister when he was 10 cause he felt like it. his sister told my freind that she didnt know what to do so she just let him shes 6 years older than us i know he was just a kid then but you cant wipe away that part of the past >:( what should i think?