I just read your message and it makes me so sad to hear how down in the dumps you are. I know you've probably heard this a million times, but I'm sure that it will get better. It seems like you've hit rock bottom right now, so the good news is that there is only one way to go and that's up. Things will get better, but sometimes they take a really long time. Don't ever give up hope that tomorrow will be a better, brighter day.
Try to keep your chin up and no matter what, always hold your head up high. The people who you speak of may look like they have it all, but if they are flirting on facebook, then they probably don't. It's human nature for people to want what they can't have and it's also human nature for people to think that the grass is greener on the other side of the fence. If there's one thing I've learned, it's that people are really good at pretending their life is amazing, even when it really isn't. It's just about keeping up appearances.
The best thing that you can probably do for yourself right now is to take a deep breath and give yourself a break because you are being so hard on yourself. I don't know what you look like, but I know from your posts and your messages to others on here that you are a good person with a good heart. Maybe I'm wrong, but I think that having a good heart is more important and better in the long run than having the looks of a super model. Beauty fades over time, but whatever goodness you have within you will always be there no matter what.
You're going through a rough time, and it's hard with the holidays. I know how you feel, you get lonely sometimes and that's perfectly ok. Just don't ever think that you're not good enough or you deserve to be alone because you don't. You will be happy one day, so focus on you right now. Be happy and content with yourself because there is an amazing man out there who will realize what a catch you are and he will treat you exactly the way you deserve to be treated.