I just learned how to conjure Arvak and love him but my question is when I jump off him he screams and disappears. I am not high on my conjure scale tree just a beginner so does that have something to do with why he doesn't stay when I dismount from him? If I build my conjure tree to the max will he stay as long as I want?

Unfortunately, he does go away after you dismount. However, if you are mounted on him after the full 60 seconds, you will still ride him until you dismount.