Disclaimer: I Am Not A Psychologist.
Throughout this site, you will find jokes about masochistic and, well, idiotic behavior because at some level that is a part of every unrequited crush. We do things that we know are not in our own best interest because it feels worth the sacrifice. For example, a sleepless night twisted among your bedsheets and shedding tears of loneliness can feel like a small price to pay for having spent an hour in the company of your Adored One, even if the focus of that time was to, say, sit with them at a concert in which their significant other had a singing role. While decisions like these may be unwise, they are nonetheless a part of the experience.
It is, however, truly self-destructive and unhealthy to obsess too heavily over another person (or oneself, for that matter). It's not simple to say what counts as "normal" behavior versus what is harmful to oneself, or what is unfair or even frightening to the person you wish to be closer to. At least, it's not simple for someone like me who is not trained in psychology. I do know, though, that it is sometimes all too easy to become a burden on the person who you want more than anything to lift to new heights, and for that reason I implore my readers to try to keep a healthy, well-rounded perspective on their situation. Helping to foster that perspective through the use of humor is, as I said in the introduction on the front page, one of the main goals of this site.
The most important sources of support in trying times are, of course, your family and peer groups. The people who love you want you to be well and want you to be happy, just as much as you want your Adored One to be. Don't be afraid to make yourself vulnerable to them, because that's the only way to let them help you. Another possibility is the Net; I don't recommend forgoing all your options in meatspace in favor of cyberspace, but don't ignore it, either. Sometimes it's easier to talk through the computer, with the level of anonymity and detachment that it affords. There are a lot of online discussion groups and websites with encouraging words and people. You can find links to a few on my Agonizing Links page.
That said, we all know that sometimes wanting to be healthy is not enough. Sometimes our friends and family can't provide whatever it is that we need to feel better. Sometimes we do Bad Things(TM) to ourselves or to others without meaning to, or without fully understanding their consequences. Sometimes, we need to reach out and ask for help, or have the courage to listen when our friends tell us that they are worried. Clinical depression, obssessive disorders, nervous breakdowns... these things happen to people. It sucks. But they happen, and they can happen to any of us. It isn't our fault, it doesn't mean that we're "crazy", it doesn't mean we're weak, or broken, or stupid, or unworthy of being loved. It's just something that happens, like catching pneumonia or suffering from bronchitis.
If somebody suspected they had a dangerous heart condition they might be afraid to go in for tests and find out for sure, but chances are they wouldn't be ashamed to ask for help or treatment. And if you suspect you may be mentally ill, the same logic should apply. Do not be ashamed. Find someone and ask for help. Seek counseling. Visit a psychiatrist. Take medication. Whatever the solution is for you, find it and do it. You deserve to be healthy. Don't suffer needlessly.
It's not unusual, or even shameful, for thoughts of suicide to run though one's mind in times of duress. On the other hand, if you're dwelling on it, having lots of suicide daydreams... if you are seriously considering killing yourself... For crying out loud, at least talk to a few people about it first. Being suicidal -- or even "less" serious forms of hurting yourself such as cutting or burning -- is a dangerous mental condition if I've ever seen one. So as with any other, as I've said above, just reach out to somebody and ask for help before you do anything. Most mistakes that we make in life we can recover from or make amends for in some fashion. But if you kill yourself, you never get to look back and decide whether it was a good decision or not. So you'd better be pretty damn sure that it's a rational course of action first. And I don't mean "Every day is pure agony," kind of sure. I mean "Every day is pure agony, there is no possibility that things will ever improve, my friends have considered my situation and agreed that there is no point in me going on and support my decision, there's nothing left in this world that I want to accomplish before the end, and I've shared mutual a 'goodbye' with everybody who will be sorry to see me go," kind of sure. Don't think you'll ever be that sure? Okay. I guess I'll still be seeing you around, then. Now, how about going to see that therapist?