I feel like they don’t know me and I have no one to talk to
...and...
I realized I’m not being the real me with anyone.
Do you know who you are yet? Its okay if you don't but that is the starting point. Entering adulthood as you are now in means you don't have to be what others previously in authority over you told you you had to be. However, it does mean you need to figure out who you are. If you don't know who you are yet, then thats a separate topic that I'd be happy to give advice on if that is what you are seeking.
How the hell do I get out of this? I’m working on myself and feeling better, but whenever I think of letting someone in, the wall come up, with all of my problems written all over it.
...and...
I guess I should be honest and go slow? But how to be open without bothering someone? Cause I feel like they might go “oh I wouldn’t have let her get close had I know THIS”
Employ empathy, and by that I don't mean "make them feel better" but rather, imagine a copy of yourself in their place, your strengths and your weaknesses (this is part of knowing yourself) and empathize with the situation. That other person isn't perfect and has their own baggage. Don't imagine them without any cares or concerns simply because they handle themselves well. We're all struggling with life. Recognize that. Instead of trying to open up to them with your problems, let them know you'd welcome to them open up to you in whatever capacity they're comfortable with (which you have to accept could be none at all). Wouldn't you like to receive the message from that other person that you could connect with them? Be that instead and be the one offering an opening.
Be the person you ideally want to be. Be the change you want to see around you.