Bottle frustrations


So my 13 month old son will drink water out of any type of sippy cup (straw included) but the moment I put milk in it he won’t drink it. I even got the transitional Dr. Browns sippy nipple to put on his bottle to trick him so he would drink his milk, BUT I gotta say he’s not stupid and is refusing it now! He just does not care for milk unless it’s in his bottle (with a regular nipple). He just always wants the bottle regardless of what’s in it... So what do I do? Go a couple days without giving him milk or a bottle? That way he forgets about the bottle? I dont know what to do at this point. I’m just afraid he won’t get the proper nutrients if he goes without milk. And if I reintroduce it in a sippy, what if he still refuses it? UGH I wish I did this sooner. I’ve been at this since he turned 1.