I will make it brief, because I am on my way to bed.
Alright, I will get a but personal here. Just last month marked my 3rd year of sobriety. It started out exactly like you describe. I was basically a normal kid, perhaps a bit introverted, but happy enough. In my early teenage years I smoked weed a bit socially at parties, etc, and would drink. No big deal really. I think the majority, although not nearly all, of people at least try smoking weed at least once in their life. Over the next couple years, smoking and drinking progressed into an everyday think. Before school, during school, out with friends after, and every time in between.
After I graduated, my weed habbit developed into an Oxycontin habit, and yeah, I was one of them "I'll never do hard stuff, just smoke weed" people, too, so saying that don't mean shit. After a few years of smoking weed, it becomes ordinary, and those other things become more and curious. I had since tried a plethora of other drugs before this, but apparently my drug of choice was opiates, because my life became a train wreck for the next 6 years.
Once you get really hooked, you will be really surprised how fast all them "things I will never do" go flying right out the window. I've broke into houses, robbed people at gun point, and did all other manners of really grimy shit to get money for my habit. I stole from my family, lied to and manipulated everyone in sight, whatever it took.
The last year of my using was the worse. Simply snorting Oxys wasn't doing it for anymore, and I upgraded to heroin. Now I have always had a fear of needles growing up, but before you know it I was turning myself into a human pin cushion. You want to talk about feeling like a piece of shit? Image yourself Think about sitting on a dirty couch inside some run-down fiends house, and watching yourself stick a needle in your arm. The whole time I am thinking "what has my life come to...?", but there I was, and that thought didn't stop me.
I'll spare the rest of the details for now, but a few months later, I went to rehab for the 3rd time, and I managed to actually remain clean. I had to get to the bottom apparently before I leaned my lesson. I kept going back to it, and here is the reason why, and the reason I made this entire long-winded post: It made me feel like I belonged. Like I said, I was a bit introverted, and although I had a few close friends, I always felt that there was SOMETHING missing, and when I did drugs (yes, even weed), I felt better. I met new people, and I felt like I was a part of that group. I was one of them. This may not sound like much to many people, but when you feel you have been lacking it all your life, though never previously defined, it is a good feeling. And now I get to the point. You can't fill the holes in your own soul from the outside. Drugs will not help fill them holes like they may feel like, they help you forget, but the holes still remain, and only get bigger. You need yo really take some time for yourself, and make a brutally honest self-inventory. Find what is missing in YOU, and find ways to fill it internally, without the "aid" of drugs.
I can honestly say that the past 3 years have been the best of my life. I have leaned much about myself, and have become honest with myself, and surrounded myself with people that will call me on my bullshit when I am not. Nothing especially "great" happened, I just learned to see life through a different say of eyes, and have a new perspective on everything. I have no idea why I chose to go off on a rant, but some things you said reminded me of my own thoughts over 10 years ago, although I didn't have the clarity to recognize it back then what it meant. I just hope this whole post is wasted, you think I am crazy, and you never take the path I took in any way, but in the off chance that it helps in any way, I suppose it is worth it.
I'm going to bed now.