I am going to pick apart what you said. My responses are in bold:

"I just wanna be happy
I dont know what makes me happy anymore"

That's because you have conditioned yourself to believe you cannot be happy. When you start feeling yourself think something negative - purposely turn it into a positive.

Ex. "I am stupid" becomes "I am intelligent and learning more everyday!"

Eventually you won't have to be purposeful about this anymore bc it will just come naturally

"Smoking weed makes me feel better and able to put up with stuff a lot more... so for more than half my life i have believed it to make me happy.."

Smoking weed will indeed cause you to feel happy while you feel the effects of it but while you are coming down from it (or if you become addicted - during the withdrawals) you will be extremely depressed

"When someone is genuinely giving me atten
tion i feel better.. wanted.. but ive put up so many walls i think that i dont think that i really allow anyone to give me attention anymore..."

One thing I had to learn is that you cannot depend on anyone to make you happy. This is because you cannot control them. You cannot control their actions, beliefs, reactions, thoughts, or words..but you can control your own. It is through controlling these things you will find the ability to in turn control your emotions.

"I dont know what i like about myself...
Everything about me seems messed up anymore and cant do anything right
I used to be kind of smart... but im just stupid now because i cant think... focus... or remember anything..."

These are the repetitive statements you say to yourself. Turn them into positives

I am not messed up. I am a work in progress.

I am still learning about myself and other things, so I may make mistakes, but I will improve.

I am intelligent and learning things everyday!

"I try to play music but fail because of my problems and dont get anywhere with that...
I just cant think of anything.."

There is no requirement to focus or think or remember when it comes to music. Just let it play. Enjoy the parts you notice. Let the other parts just "float"

"I understand what you mean though.. and appreciate it.. i just scared that maybe its too late.."

Nothing is ever too late unless you deem it too late in your own mind.

"I need real friends... but i have never had real friends before so i dont think it will happen now.. especially since i have so much trust problem..."

Friends cone and go. You don't. Always remember to be there for yourself. Love yourself. People are attracted to those who love themselves.

"Im just scared that its over"

It's over when you say it is - not until.

"My mind keeps replaying things... how ****ed up i am and how weird i act... things i said or didnt say... everything i done wrong... or thought i should of done different..."

Again turn these into positives.

I make mistakes because I am human, it's ok to be human.

I am allowed to say and do whatever I want to or don't want to. If I hurt someone, I can decide to apologize. This will happen at times. It happens to everyone. It's ok.

"I just want to run away, to disappear."

What would disappearing resolve? Your issues would still be there.