So I have a guy friend who I liked, and I decided to tell him I liked him, and he SAID he liked me back (and asked me out). Then an hour later he dumped me over text saying "I jumped into the relationship too fast" because he got dumped by his gf of 8 months (and for freshman in high school, thats a REALLY long time) so I totally believed it no questions asked.
My friend decided to ask him if there was any chance of us getting back together and he said no. And when she asked why and he said "I never even liked her I just asked her out because she told me she liked me"...
And now it's just REALLY awkward and he makes no effort in conversations and if he doesn't then why should I?

Why would he screw up our friendship by asking me out then dumping me within an hour? And why would he say he likes me and ask me out if he didnt?

You said you liked him. That already made things awkward. He would feel like a jerk if he just said "Oh, I don't." This has happened multiple times with people I know. It's ridiculous. He shouldn't have asked you out, but at the same time, you did sort of set him up. Either way he comes out as a jerk, so, by saying yes, it's just the easy way out. Then he probably realized it was a stupid idea and dumped you. Put yourself in his shoes, you'd feel like a jerk if somebody said they liked you and then you said you didn't like them back.