What he did was abuse and it was not your fault, so you should in no way blame yourself.
Often this type of behavior at the age he was though would be indicative of him being abused by an adult or another kid who was abused. The loss of power they feel as a result of said abuse causes them to abuse others in order to try and feel powerful. When not dealt with, this can often lead them into repeating this behavior into adulthood. Someone I know found out that someone who had assaulted them had first assaulted another person at the age of 11.
If I were you I would try talking about this with your parents, and I would avoid being in situations with this person were there are not others present (or preferably avoid this person completely).
Your safety should be the number one priority.
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22, entrepreneurial and diagnosed with High Functioning Autism, ADHD, OCD and Tourettes. Also have problems with Anxiety, and more recently depression, although I seem to returning to my optimistic self =)