Somebody plays the flute (?) very well; you desire to have the same skill but you can’t. You are not really jealous of the other person. I think you could simply use the word 'jealous' in an admiring way - it doesn't have to be negative: ~ I'm really jealous of your skill, it's amazing! or: ~ I really admire your skill at playing the flute...

I also agree with Charlie. 'Jealous' and 'envious' are not necessarily negative in English.

I agree with Charlie. I admire your skills. I'm so jealous of your skills. I envy your skills. I'm inspired by your skills. I look up to you. Someone plays the flute well. (You need to include the article before the instrument).