...how deep could my feelings be towards a person I met 3 weeks ago?
Bless...you're 18, you have a MOUNTAIN of living to do, and many many experiences yet to come. I saw an interview with Michael Caine (famous actor, which you may know) a few weeks ago. In the interview he said that he saw his wife for the first time on a T.V commercial and said to his flat mate...THERE SHE IS! "I have to find her, I want to marry this girl". The flat mate said back to him..."What are you, mad?" So, Michael Caine went across to the other side of the world after trying to locate her, and guess what? He did exactly what he set out to do. They've been married ever since. In fact, he said in the interview, that he still loves her as much as he did then, if not more. Love can, and does happen that way for a proportion of the population.
You know, I remember overhearing a conversation between my mother and her friend shortly before my wedding (almost 30 years ago). They didn't know I was almost ready to walk into the room, so they didn't know I was there listening. I overheard my mother's friend say to my mother...
"what will happen when she falls in love?" Hmmm, at the time I didn't understand what she was on about or why she would've said that. Whilst I knew I didn't love my husband to be, I didn't know what love was. Like you, I thought to myself...what else could there be, I had companionship, sex and support. Easy peasy

AND, you know what happened as the years rolled on? The "weak basis of the relationship, meaning companionship, sex and support became much weaker as time went on. The sex became INTOLERABLE. I'd cry every time he wanted to touch me. Why? Because there was no chemistry (albeit, I didn't know exactly what that meant at the time, so nothing to compare it to), so during times of insecurity, as my ex husband had - his paranoia mixed with complacency, as well as his inability to ever say "I love you" - became toxic. We were friends, but he wanted a 'mother' not a wife, and so many problems arose as time went on. I became angrier and angrier, which in the end killed the sex and the caring. In other words...there was NO foundation on which to fall back on, only a frame, a couple of windows and a roof. The windows were solid, and so was the frame AND so was the roof, BUT, If there are no foundations, all of it will cave in.
I'm not going to speculate X's thoughts or even behaviours any more. He IS NOT the Michael Caine story I was so hoping he'd be 20 years ago. He's not even almost close. He no doubt wants complacency and subserviency. Good luck to him. It's as boring as batshit, but hey... some people love to live boring lives. What they're really doing of course, is locking themselves away in their cage of fear. There's a quote, but can't remember it exactly, however - it says something along the lines of ..."those with the picket fence, 2.5 kids who go camping once a year and get the gold watch after working for 50 years in a bank, are mad!" In other words, living a life in a straight jacket is not only an anomaly, it's pathological according to both Salvador Dali, and Einstein. Anyway, hope all this makes sense.

Good on you for recognising your situation, it's a good thing, not bad.