I am confused?

Ok so this guy who I really like at work, seems all interested when we talk and when we see each other at work...the only problem is that I am the only who seems to call him he doesn't call unless I call him and he misses the call, or he calls rarely like once a week or something, at work he is very attentive with me and flirts alot, he has even given me a ride home, I just don't get why he doesn't call or he's always busy as he says, but when I call he'll talk to me for a long time, I am majorly confused because if he was interested wouldnt he call more??