Hi B.,
Your son sounds normal for a baby who hasn't had all that much practice with bottles/sippy cups due to breastfeeding, and I'm sure he'll pick up the skill with no problem in the next few months. He's enjoying your help/attentiveness now, but very soon he'll want to do it all on his own, and you'll be at your wits end with that, too!
In the mean time, if you want to hurry him along, remember babies learn the most by imitation. Make sure the time he spends with you includes you modeling what you want him to do...make sure he sees you drinking from cups (adult ones). If you really want to reinforce the lesson, fill a sippy cup for yourself and model drinking from it with exaggerated sounds and movements that will catch his interest: "Whew, Mommy is thirsty! I'm going to drink some water from this sippy cup. Watch Mommy: I lift it WAYYYY up, and GULP GULP GULP, ahhhh! That's better!" My daughter learns so much just from watching us go about our daily lives--it's taught us to be careful what kind of ordinary behavior we're modeling for her!
J.