Do not give him anything in the middle of the night. Do not teach him that you will respond to his ridiculous requests. No discussion! If he wants something, repeat the same answer over and over again. E.g. "No, it's the middle of the night, go back to bed." Remember, you cannot reason with a child in the middle of the night. If he wants water or food, just tell him "No, it's the middle of the night, go back to bed" or whatever you come up with. It has to be the same answer over and over again as he will get tired of it and get the message.
If he has had a drink before bed, he does not need anything in the middle of the night. Do not teach him that it is worth waking up. And do not feel guilty about being the "bad" parent. Your son will remember, when he is older, who did what was best for him.
And whatever you do, do not mention his dad unless it is something nice. I got so sick of hearing my mom complain about my dad. When my mom finally accepted the divorce, she would speak well of my dad. They got along so much better then and it so much nicer for us kids. What do you want your son to remember about his childhood?
In order to get along better with his dad, be sure to compliment him on something that he does with your son every opportunity that you can. It will go a long way with your relationship if you demonstrate some respect for him (no matter how hard it is to do it!) and your son will benefit in the long run. Even complimenting his dad to your son will make him respect you more!