How to handle jealousy & negative competitive behaviour

I have been applying my teachings from this course they have been great but we are a work in progress. Something came up this week that I wasn't sure how to address. My 15 year old son showed extreme jealousy when his friend showed the same advanced skills at playing guitar as my son's. His immediate reaction was negative and not comfortable with someone else sharing that skill at his level. He also showed a negative competitive behavior about volleyball (his current sport that he plays in a competitive club). He wants to be known as better than other players, even though it is his first year and just wants to prove himself rather than excel in a healthy competitive way. I feel like the two situations stem from the same underlying issue and I cannot figure out the best way to guide him. We had a talk about being happy for his friends and the difference between toxic and healthy competition in sports and focusing on a win-win mindset.

FYI, I edited my profile with my brief story and picture but it is not displaying on my end so I hope it is on your end!