I'll do to that person what I do when it's me who feels envious or 'insecure' about something or someone - I'll keep my distance.
If that person I'm having that feeling towards is a friend or someone I like, then lilipas naman yon after some time.
Hindi naman maiiwasan ng tao makaramdam ng inggit, or ng insecurity at times. Even the seemingly happy and contented people feel that too. But what really matters is what people do about it. If si friend is insecure and I feel it lang, though she's not doing anything hurtful naman to me, I'd just put a little space between us. And then eventually, if she's a true friend, for sure, that feeling would be fleeting naman. And I as a friend din, will point out in the most subtle way (yung hindi halatang sinasadya.hehe) the great things about her life para maramdaman nya na what she has is just as wonderful.
If for example naman the friend does something hurtful and offensive as a result of these feelings, then ganon pa din, keep my distance. Pero siguro for a longer time - and literal na quiet lang talaga ko, no reaching out muna. Kasi if she acts like that because she was just insecure/envious means may deeper issues sya na kailangan isettle, maybe with herself, or perhaps between the two of us. But the space/distance will certainly help clear the air first for possible talks in the future about it. This is given that she's a true friend ha.
If we don't talk again ever, and she stays insecure for the longest time - well, alam na.