Happy 18th birthday!
You're not gonna suddenly become an adult at 18; Like, you're not suddenly gonna have the expirences adults have over 25 ....
Most 18 year-olds don't know anything about what to do, where to go, or what they want. Even if you're 18, you still have to work for what you want.
If people look down on you, prove them wrong by living and showing them what you can do. As someone else posted here, there is much more to live for. Don't give up on it!
Don't let anyone make you think differently; Only you can make GOOD things happen.
And most 18 year-olds are afraid of adulthood. But it's not something that should make you suicidal; Even if it's hard to imagine, there are things to enjoy in life. Don't let finances or people make you feel hopeless.