Why do I feel like my friends are pushing me away?

First of all: you shouldn't think your friends are pushing you away all of a sudden because you don't hang out all the time and they don't invite you to stuff. If you see that they're comfortable with you, that they enjoy in your company, that's all that matters, try not to overthink and everything's gonna be fine :)

Second of all: don't self harm. I know once you get used to it and letting the anger out like this, it can be hard to quit. But you must. It's not good for your body and neither is helping your mind or makes things any easier. So try another way of dealing with things; try relaxing things like yoga (you may think it's foolish, but it really helps!), go out for a walk, read, write... There are really many stuff.

But if you're still in a dilemma about your friendships, go talk to them. Ask them nicely and they'll tell you nicely. It's not gonna necessarily end bad, be positive and calm! :)

Don't feel bad, but if u want to konw if they really are your besties or not, then when u again arrange a party do not invite them, but u have to make one thing sure that they know you have arranged a party, and when u see them again after party, they will say something y didn't u invite them, so then u can tell them "this is what u got for what you do." And I would prefered to make new friends, because true friend always invite each other no matter how bad you would have done to them, as long as you invite them.