Weekend girlfriend?

I've been dating my boyfriend for almost 9 months. Why the hell is he a completely different person during the week. Doesn't call or text as often, and he's not as nice. Says he's just tired from work or whatever, very snappy....during the weekend, he's soooo nice to me when I'm with him...and even when I'm not at his place over the weekend (at work, or at home) he communicates more.