There's this guy who really liked me and I always treated him so bad never cared, I also spoke to his mates which he didn't know about, now he's stopped talking to me I always try but he never answers or anything and I realised I like him now :(

Never assume guys don't talk to each other and looks like you missed the boat with him because you realized too late you should have been nicer from the beginning. Back off now and stop chasing and talking to his friends about him as you look desperate. That will never work for you.

Sorry but for now you have to leave him alone and see what happens. Look around for other things to better occupy your time and mind with. How old are you both?

I've stopped talking to his friends ever since, and I've never spoken about him with his friends, I try to do so many things but I can't forget him its so hard. I am 20 and he is 21 </3

This is what happens when you are not nice to people.
Move on and be nicer to people in the future.

I understand I took advantage of his niceness, but he always gave me mixed messages sometimes he liked me sometimes he treated me like a friend.

That's not a mixed signal, just a friendly one, and not a reason to be less than a nice person.

So I must forget him now? :(

That's best so you can get back to having fun again and enjoy a happy healthy life without him for now any way. Who knows what happens later.

:( thanks

I just don't want you to sit and be sad over this that's all. That won't help anything and sorry it didn't work out.

He was interested, you weren't. You treated him badly, and he stopped talking to you. Now that he's not interested in you, you're suddenly interested in him. When you said you're in your 20's I was shocked, I really expected you to be 14 or younger, because this is a game young teens play, not adults.

Sounds like he decided to spend his time with people that treat him well. You didn't.

Time to move on, and next time, treat people better, even if you're not interested, because that's just the right thing to do.

I didn't treat him bad bad its just that I wasn't too nice I was very reserved because I was scared of attachment due to past experiences I've never had a good relationship so I find it hard to accept that someone will generally like me

You said you treated him so bad never cared. Now your saying you didn't treat him bad you just wasn't too nice. Same thing. To treat someone less than nice for no reason, is treating them bad.
You need to get yourself together as you may not be emotionally ready for a relationship anyway. Work on yourself first.