Several of my friends are dentists and they all told me that sippy cups are worse than thumbsucking or bottles when it comes to their teeth development (it's hard plastic that doesn't 'give' like the others). I was told to stop the sippy cups by 18 months - 2 years at the latest. It wasn't that hard. My kids were using regular cups at meals and snacktimes by 12-13 months old. The first few times there were spills but since they only get water at meals it's not a big deal. They use a sports bottle for water during the day to have near them when playing or in the car.
As for taking it away - just do it. Of course he'll cry. You've let him hang on to it far too long and he's grown attached to it. The longer you wait, the harder it'll be. It's better for him in the long run - you know that. He doesn't. He's the kid. You're the parent. He'll cry for a few nights and get over it. And he'll probably get over it faster than you think as long as you don't give in. Chances are, he'll be asleep by the time you come to bed.
As for not being able to stand to see him cry.... my kids are older now and I'll tell you that you better get over that. None of us like to see our kids cry but sometimes we need to make decision that is in their best interest that they do not like and they WILL cry. And they WILL say "I hate you" a few times. And you better NOT cave in when they do because when you do, you just reinforce that in your family, the kid is in charge and not the parent. Stand firm so your child will respect you - kids are looking for boundaries (even if they do cry when they run into them!).