Yea... you should never be envious of others because you loose sight of what you have. Sure you might not have the equipment, but you DO have the knowledge of how to use it. I rarely EVER find myself being jealous of anything anyone has because A) I don't work for my things, honestly my parents buy them for me (cash and I get it but you get the picture) (I just turned 18)
and B) What good is it going to do? I honestly try to be friends with EVERYONE because you never know what good is going to come out of it. I'm literally on speaking terms with about... 90 percent of the people in my classes at high school and if I needed a ride home (which I often do because I don't have a car), 80 percent of the people who drive would gladly give me one if they could.
I'm not bragging because there are obviously people who are in high school who have more money, more friends, and a car (lol) but just be grateful for what you have because you never know what can happen tomorrow.
But yea... at least use the equipment haha.... and instead of being mad at him why don't you help teach him about this wonderful hobby. The way I see it, if I had a rich friend with a lot of headphone equipment I'd definitely help him with the hobby. Helping him would probably = borrowing his stuff cause he's your friend (hopefully) and most importantly helping someone discover how AMAZING this "hobby" is.
Didn't mean to sound long winded or an optimist on this one, just my 2 cents on how I feel.