I haven't been banded yet so I'm not speaking from experience yet but I think you are being too hard on yourself. You are human and it's only natural to indulge a little, especially this time of year. I personally think that it is ok to have a treat now an then, it's when you are so strict that when you have a slip you fall all the way down is what got most of us to where we are. I think that if you are feeling like you are on a diet then you are approaching it wrong. Remember weight loss is about burning more calories than you take in. The problem with bad calories is that they don't give you the energy you need to be able to burn them off. Don't feel bad about having one chocolate covered cherry, just be happy that you can't eat 10 or 15. It's feeling bad about that one that will lead you down that bad path.
Also there are a few thread about eating and drinking at the same time and it seems that most people like you have a sip or two while eating. Like you I think it is unrealistic.to not drink at all but as long as you are drinking no more than a small sip or two then you are ok.
When it comes to the pizza don't get too upset about it, first of all think about how much pizza you could eat before the band, now think realistically about how much you could eat now. Did you go from 3 (or possibly more) slices to 1/4 or 1/2 of a slice? If so that the power of the band, think about how many calories you just saved, realize that if you do only have 1/2 a slice that you will feel as full as you did before the band, and still have the same flavor. I don't think that there is anything wrong with taking a slice cutting it in half and eating the cheese and toppings first (protein!) and maybe a bite of bread if you know you can handle it. If you also plan your other meals of the day around that then you will not go over your calories, you can also build in a little extra exercise for the pay (park a little farther away or walk a little faster than usual)
Your experience at Cheesecake Factory is a great example of how great the band is, you were able to eat out with a friend, have a totally satisfying meal, and didn't have a boat load of calories. I went to the Cheesecake factory this past weekend and I'm pretty sure that I blew 700 calories before we were done with our appetizers.
It's good that you realize this early that you might be becoming obsessed with food in a bad way because now you try to stop it before it becomes a problem. I think the first thing to keep in mind is remembering how much you could eat before and how impossible it is to eat that much before. Also if I remember correctly you haven't been cleared to exercise yet so that hasn't been able to help you yet so imagine how much more you will lose when that comes into play.