Kevin let me tell you something, when I was your age I was VERY like you. I had not had much contact with women.. I was scared to even really be myself around them. It's depressing as hell.. tell me about it. I'm sure your watching all your peers flirting around with girls... and you hear the stories.. but it's just not happening for you.
Let me give you some good news. Life gets A LOT better. I'm 20, finished high school and working - Life is very good! I've become a lot more comfortable with women and I'm living a more healthy life style.
I think you're doing alright - your working, getting exercise, doing reasonably academically.. Your "only "issue" is that you feel unsatisfied with your social life.
I know this is gonna sound like a load of BS - but waiting for a girlfriend is like waiting for Christmas.. the waiting is part of what makes it so special. Without all that waiting you wouldn't enjoy her as much as you will when you finally find her.
Now a little advice, when you see a girl you like.. don't be afraid to bite. Women enjoy attention, you don't have to be mr. smooth, or mr. smart, or mr. tough, just talk to her. Don't turn down a girl because you think she's too young for you.. or too old for you.. just do what makes you happy.
Women aren't that big on looks, my brother is a tubby ugly arrogant ass - but he gets lots of women, because he's confident and he can make them laugh

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Your not a big Loser, and no I'm not sugar coating anything for you. I'm giving it to you how it is. Your really just feeling a bit down because it sucks not getting laid. It's alright tho - I guarantee - just keep living a healthy lifestyle and things will come naturally!
Honestly, it's much easier to ask a girl out then to kill yourself. Let me tell you something Kevin - you can ask out any girl you want

- there's no rules, no standards, nothing. You don't even half to know her name.
anyways.. there's really way to much your gonna learn over the next few years for me to try and explain. But I'm telling you one thing- IT GETS BETTER - KEEP TRYING.