I'm almost 19. My mom starts the biggest arguments with me even when I'm talking to regular friends on the phone and says I shouldn't be doing that at all. She doesn't know that I have a boyfriend and I'm afraid to tell her knowing how she reacted a few months ago when I told her that him and I were friends. How can I make her realize that he's not going anywhere???
Your parents will probably never stop trying to exert control over your life, even when you move out. But at some point they have to realize they can't control everything. I mean, they probably let you work the stove now, right? You aren't two years old.... So show them you are mature enough to handle it.
If you are lying to them and sneaking around, they know something is up. I'm not saying they know every detail, but people usually can tell when someone is deceiving them, and will treat them accordingly (consciously or subconsciously).
It seems like you are in a cycle now.... They don't want you to date because you are not mature enough, and you think you are mature enough but since they prevent you from spreading your figurative wings, you feel like you have no choice but to go behind their backs, making them trust you less.
So break the cycle. First, is this guy really worth all the trouble? Most teenage romances don't last, because so many life changes happen. Going off to college, job transfers, etc. If he is your dream guy and you two see a future together, bite the bullet and bring him home. Cook your family a nice dinner and invite him over. Have him shave and get a haircut and dress respectably, nice shirt, shiny shoes, the whole bit. The idea here is not to fit you or him into any mold, just put on a good show so your parents give you a little more freedom.
If dating this guy is more of a defiance move against your parents (answer this... Does he smoke pot? Does he have lots of piercings/tattoos? Does he drive a motorcycle? Yes to any of these suggests you like him because your parents don't), then just break up with him, and maybe find a new guy. Seriously, it won't last anyway. Sit down with your parents, talk to them, tell them how you feel smothered and you need more freedom.
They will likely reply that with freedom comes responsibility or something to that effect. Fair enough, you'll just have to wheel and deal. Take on more responsibility, but not more than you can handle. Get a job. If you have a job, discuss getting a promotion with your boss. Maybe take an advanced class at school. If you're not in school, maybe apply to some school that would challenge you and help you achieve your dreams. When they see that you are taking responsibility for your own life, they'll probably be glad to cut you a little slack.
Parents don't have children in order to keep them children forever. Most parents would love to see their kids grow up, get married, have kids of their own (payback!). Unless arranged marriages are their thing, they realize dating is a required step in this process. By the time you reach 18, they are pretty much sick of you. But they still don't want you to end up doing something stupid to ruin your life or kill yourself, so they can be a little overprotective.