1. No one on this forum is qualified to help you if you are really depressed/suicidal. Here are links to lists of psychiatrists/counselors in Seoul.
http://koreabridge.net/discussion/counselors-therapists-psychiatrists-counsellors-seoul-areahttp://forums.eslcafe.com/korea/viewtopic.php?t=242292. If this man, your "crush," never admitted to you that he has feelings for you, and got married to another woman, AND had a baby with said woman, perhaps that means he did not want to be with you. That doesn't make you any less of a valid person/unlovable/etc, it just means that either (a) He just didn't like you, and all the body language you've been describing is because he's nice and embarrassed and awkward and flattered that you like him, and he doesn't know how to respond to it, (b) He liked you a little also, but liked his new wife more, or (c) Perhaps he didn't think you'd want to stay in Korea being a subservient daughter-in-law, or his parents were pressuring him to marry a Korean woman.
Or there could be a million other reasons. And marriage doesn't always happen because of love, nor does it have to.
As for your co-workers, unless you speak fluent Korean, I'm not sure there's any way you can be 100% that they're making fun of you. Many of my coworkers laugh "at" me, but what they're actually doing is laughing at themselves and their attempts to talk to me. Besides my coteachers (who are older males, and as a younger female we don't do much "bonding"), my coworkers don't speak a lot of English, and I don't speak a lot of Korean, so communication requires a bit of finagling at times.
Also, the whole "OMG, I'm going to die alone!" I suppose is a legitimate concern, but with the miracles of modern technology people are living longer and longer, and waiting longer and longer to get married/have babies. My fiance will be 40 in May, and he's never been married before. It just didn't happen for him.
Also, looking for someone else to make you feel like a complete person is a terrible idea. You're putting your happiness in the hands of someone else? We can't control other people. Don't give them that power.
Here's my advice:
1. Talk to a professional.
2. Quit the school you're currently working at, because unless you get a major attitude adjustment it doesn't seem like you'll enjoy yourself.
3. If you want to teach ESL, find a better job in Korea (yes, it IS possible), or in Thailand, or Laos, or Vietnam, or China, or one of the other scores of countries available.
4. If you don't want to teach ESL, go back and hang out at home. It's awesome that you have parents that would let you chill out while you thought your life over. Go home and research more life options, and find maybe find something new to try.
5. Use meetup, facebook, or one of the millions of other internet websites to find friends in Korea. Where do you live? I'm sure there's another foreigner within a short bus ride. They might not be your ideal best friend, but let's face it, options are limited here. But they might at least be fun to hang out with. Join a club or class or something.
6. Stop concentrating on how attractive you are. Attractive does not equal interesting, funny, etc. Being attractive does not automatically make life easier, you still have to work at it. People only want you to *think* attractive = easy so they can make you buy stuff.
7. Build up your self-esteem, find your own interests, and maybe while doing something you love you'll find someone with similar interests who loves you too.