I'm not made jealous easily. I do remember feeling resentment after an ex unceremoniously dumped me years ago, and quickly moved onto new girls and would look right through me and keep walking when we saw eachother again, while lavishing attention on someone else and filled with laughter. I think he meant to get under my skin honestly. In perspective there was nothing to be jealous about. He was actually a narcissist. The way he treated others was very unbecoming, and feel sympathy for others he may have emotionally abused.
I don't have much experience with jealously though, envy is a little more common, but still not unusually so. Sometimes I envy people when they have opportunities that I didn't. Something as simple as having a stable household with both parents in it and brothers and sisters wasn't something I had growing up. So treasure that if you have. I feel the same way when someone I know is in a college program. It was a hardship for me to do any type college, and I'm still in debt from it. There are times where I wish I could have been dealt a better hand in life. At the same time however I don't harbor another more fortunate person Ill will, I might just feel wistful for a moment, and then carry on, content with what I have.
When I was single or in relationships that were crumbling the sight of affectionate and passionate couple together holding hands, kissing and cuddling, or even just a man at the store thoughtfully buying some flowers for a lady would be bittersweet.
Such are the little touches that just make us human.