Lol I'm 18 and single!
My apologies if I undermined the seriousness of your post, but I'm guessing my situation is different to yours because I'm incredibly ugly and repel men and women alike with my looks and awkward personality.
Personally I've been ugly since I was 11 and spent alot of time stressing about whether I will or how I could get into a relationship as growing up, boys around me were bagging girls like they were fishing. Being catholic, I turned to the bible and it gave me excellent quotes:
1 Corinthians 7:32-35 ESV
"I want you to be free from anxieties. The unmarried man is anxious about the things of the Lord, how to please the Lord. But the married man is anxious about worldly things, how to please his wife, and his interests are divided. And the unmarried or betrothed woman is anxious about the things of the Lord, how to be holy in body and spirit. But the married woman is anxious about worldly things, how to please her husband. I say this for your own benefit, not to lay any restraint upon you, but to promote good order and to secure your undivided devotion to the Lord."
I realised that being alone doesn't mean the end of life and that I could enjoy life by myself too. Relationships are absolutely gorgeous but it does require sacrifice and compromise. Being single, albeit lonely, offers independence and much freedom. You get to explore, enjoy and perceive the world through your unique, unbiased perspective and it truly is a wonderful way to experience the miracle of life!
Being single also gives you more time to enjoy hobbies such as driving, taking relaxing walks, playing games, watching clouds go past and enjoying nature.
I think that the first step to overcoming your depression is to recognise that being single isn't the end of the world, rather just a different road in the journey of life.
Also don't be envious of your friends and there relationships. Be happy for them and their partners, as jealousy is evil and inhumane.
James 3:14-16
"But if you have bitter jealousy and selfish ambition in your hearts, do not boast and be false to the truth. This is not the wisdom that comes down from above, but is earthly, unspiritual, demonic. For where jealousy and selfish ambition exist, there will be disorder and every vile practice. "
Nonetheless the fact that you have female friends doesn't mean you repel females, therefore YOU CAN GET A GIRLFRIEND! Just change your personality, appearance and physique through a makeover and exericse. Perhaps start afresh? Look for girls, not within your social network, e.g. perhaps at venues in your community such as at the library or a more social environment.
This however does require you to take the first step so refine your social skills and be kind and casual when you approach them.
I honestly don't think you are hopeless. You need to think the same thing too!
Best of luck friend! (and remember that it isn't the end of your life if you do remain single)