If you’re an adult then legally you’re a tenant, and you have all the rights of a tenant living with a landlord. Given that you almost certainly don’t have a written contract, there aren’t really any additional terms she can impose that go beyond a standard tenancy agreement.
To be clear, most jurisdictions treat a tenant living with a landlord slightly different to a tenant living privately in a separate property. So if you want to look up your rights for where you live you need to make sure it’s for that kind of cohabiting situation.
However, your mom can’t just kick you out, legally. She has to formally evict you using the same process any other landlord would evict their tenant. If she did kick you out or change the locks, you would be within your rights to call the police and have them mediate to grant access to your home.
As a tenant, you are allowed to have guests over. Not just waiting outside or on the driveway to pick you up, but inside and maybe even occasional overnight stays. Although again this may be where living with the landlord makes it slightly different.
All of this is underscored by the non-legal parts - your relationship with your mother and your continued tenancy. She can evict you, and if you fall out then she may well do that. Just because the law is on your side doesn’t necessarily mean your mom will want or have to maintain a relationship with you. A balanced position might be to assert your rights while trying not to be a dick about it and offering a fair compromise with your mom. I would say meeting your boyfriend in your driveway is a reasonable compromise, however she might not see it that way.