Ok so my boyfriend and I are getting serious and he now whats to go to the next level (sex) but i'm just not ready for that yet and now he gets mad whenever i say it. how can i tell him that i don't want to go further without getting him upset?

I guess there's no actual way to tell him without getting upset so i suggest you tell him that your not ready and if he keeps pushing this then its over. if he really loves you then he'll wait and if he doesn't like that answer then honey its time to kick him to the curb.