Hey, the Army is one way to escape from illogical parents. But I'm glad you're asking the disadvantages so you have a balanced and informed understanding of what you're getting into here.
At 18 you are legally an adult and can join. You can usually leave within a few months of enlisting. They have to do a background check on you, you have to pass a physical exam and entry exam (called the ASVAB.) You shouldn't have any problem with it, you write pretty coherently.
Housing is free. It's military barracks, but it's not that bad after initial training, sort of like college dorms, only you have to keep your room clean or a sergeant yells at you.
You can attend college on your own time. Whether or not you have any time depends on your job and your unit. Some people have time, some don't. Some places have associate's level classes on base or nearby. Or you can take online classes. You'll maybe get through three classes a year, four if you make it your priority. Army's tuition assistance should cover tuition, maybe not textbooks.
After you are out you can use the GI Bill. That will cover in state tuition plus assistance with rent and living expenses. Some private universities have an agreement with the VA matching these funds, so you can also go there for free. So you can start your degree in the Army, and finish it for free afterwards, with enough for living expenses, so you won't have to worry about dealing with the parents.
You get paid on a monthly basis, with a paycheck once every two weeks. It's not great, but it's more than enough, considering you will not pay for housing or food or health insurance, that's all completely covered while you serve. Which is the benefits.
You will go to Basic training, then job training, then to your unit. You will deploy with your unit, not as an individual. Which is good, you will know the people you go to a combat zone with. You cannot opt out of wartime service. There's a chance you could serve four years and not go anywhere dangerous. But it's more likely you will deploy, at least once.
Minimum years is about three - but total military obligation is 8 years. So if you serve three, you are in some version of the Reserves for the next five years. You could be called back up for another combat tour during that time. Again, it might not happen, but it's possible.
I think the fact that you could get called up for war is the main disadvantage. Also, the military lifestyle in general is not easy. You get up really early, you work hard. You put in long hours during field training and deployment, though it's basically an eight hour day (not counting meal breaks) if you aren't in the field or deployed. You have to do as you're told.
As a non US citizen, not every job will be open to you. But you can apply for citizenship really soon after enlisting. If you deploy, you can apply the day you arrive there, and be a citizen within months. Then you more jobs will be open to you. TELL them when you enlist, if you speak French or any other languages. Once you have citizenship, that could open a few opportunities for you.
Anyways, that's everything I could think of. Sorry it was so long. But you deserve to know what you're getting into. Thanks for considering serving your country - or one of them. :)