See, some guys aren't dogs, he might just be just looking for a friend. Don't mistake a friendship for a love affair. Also he could be waiting for the right time to break it off with the other girl and start something with you, and that's OK, Give him time. I don't want to tell you just follow your heart because sometimes your heart leads you into a dead end alley. But follow your heart and be mindful of your senses.
Women have natural instincts about everything.
The fact that he really enjoys your company and calls your more than his current girlfriend could mean that he either treats friends and significant others differently when it comes to how much attention he gives them, or he isn't very happy with his current relationship. In both cases, you still need to keep it on a friendship level with him. If he gives you a little more attention because you are one of his good friends, then see it as just that. If he and his girlfriend are having problems right now, then that's something that should stay between the two of them. Even if you feel there is something wrong, you're obviously going to look at their relationship from a biased standpoint, considering the fact that you have a crush on this girl's boyfriend.