I think jealous is a combination of hopeless and anger. Here's this person you can't have and someone else can. You still want him, still think you should be able to have him (after all, someone else has him, why can't it be you?) so you're stuck.

Find the hurt and anger that someone else has him when you wanted him and do something about it. Anger is just the feeling that we have had something of ours taken from us, we have been "slighted" or made to look silly (and we're not!) or dumb or whatever. In this case, another person can't really be "ours" which is where the "hopeless" comes in, the object of our affection has a will of their own and has chosen someone not us and we know the other person they've chosen isn't as good as us but maybe we're wrong; what if there's something wrong with us? We haven't been chosen so there much be something wrong with us or we would have been chosen!

Back up the bus to the anger. We-weren't-chosen! How dare they not choose us! But, they didn't! So, we obviously have to move on as we cannot change what another person does/chooses. So, first you realize that the other person has a lousy choice mechanism or they would have chosen us If the other person didn't choose us, there must be something wrong with the other person! (not literally but to "our" internal point of view! We should always be #1 in our world). If there's something flawed about the other person, we don't want them, they're obviously not the one for us!

So, we've gotten half of the problem solved; the person isn't the one for us but. . . how about the anger part about them not noticing how awesome we are? Well, we obviously have to think of another, better way to show our awesomeness! Now, we can do that in two ways; we can go look for and find the guy who is "right" for us and together we will be doubly awesome so others will notice or we can look at the rest of our life, our interests, abilities, and activities and put together another indication of how awesome we are. We can work harder on our school work and get straight A's, we can decide what we want to do when we graduate and set up how to become good at that craft/occupation and start on the road to awesomeness that way or we can work on getting healthy and fit so we physically shine; we can go in any direction we wish, all we have to do is turn that way and start walking in that direction. Before long, this experience will be left behind, like last year's teachers.