Commitment issues ?

I've been with my partner for 2 years now & he keeps making excuses not to move in with me. We both still live at home, he's 24 and I'm 21, both have stable well paying careers and could easily afford it, but every time I even mention living together he gets mad or makes an excuse why we can't. He's lived out of home before but I haven't. He knows how much it upsets me and just makes me feel like he doesn't want to live with me. Anyone else ever have this problem and/or know how to make him understand why it's such a big deal to me? I feel like we are never going to take the next step in our relationship ?