Please do not interpret this apology as support for your position. I am a father whose son just went through a life-threatening illness. He almost suffered congestive heart failure once due to chest cavity fluid, and could have easily suffered brain damage at any of several different crises during his illness. I could not imagine having my child suffer a dehibilitating injury to the brain, and then having his spouse wanting to starve and dehydrate him or her. Even worse, you seem to want to do it. Any reasonable person who didn't desire the end result of death would have given up by now.
It may be that Terri did in fact tell you that she wouldn't have wanted to live in a state similar to what she is in now. It is suspicious that no one but you heard it, but let's leave that to the side. Many people, including Sarah Scantlin, have recovered from being in worse condition than Terri, and returned to a reasonable level of mental and physical function. I've found that most people who have been physically or mentally dehabilitated do want to keep living like they are, even if earlier they'd said they'd rather be dead than dehibilitated.
I can understand where a selfish side to fulfilling Terri's wish would work its way in. She is very clearly not the same woman she was when you married her. You've managed to move on already. You have a new wife (you may call her a girlfriend, but if it quacks like a duck...), new kids, and a new life. You have moved on past Terri. There are others who are more willing to shoulder the responsibility that appears to weigh on you. Please let them.
What would you want for your child, Michael? Would you want your child starved and dehydrated to death when he could be treated and have some form of life? If not, then why do you ask Terri's parents to suffer the same fate.