If someone is bullying your or someone else, please file an Xbox Complaint against them then block them. This will allow the Xbox Policy and Enforcement team inveterate and handle the issue.
Acting out could result in both of you with an enforcement action, as your both then breaking the Code of Conduct.
If you know the other person in real life, maybe contacting your local authorities could also be the best option as well, as Cyber bullying is against the law in the UK and EU (Don't know about US and other countries).
You could also set family safety setting to keep him safe as well. This is what I recommend at placement with parents and in IT classes.
Hope this helps,
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