I think in the beginning, it was more "hey, let's just confuse the jury and make them think that there could be another possibility here, like George could have possibly done this." He wouldn't really have to fall on his sword, just be used as confusion and reasonable doubt for the jury. So in essence, he wouldn't really be under the bus.
Then Casey brought in the accusations of sexual abuse, and Cindy tried to make it look like George knew more about the smell than she did or something to that effect in the 911 hearing, and I think George realized he wasn't going to be used for confusion and reasonable doubt. Instead, he was going to FULLY be thrown under the bus to free Casey. I don't think he likes that one bit, and I think that's why he stopped coming to the hearings. He never planned on really sacrificing himself for Casey, but she was more than willing to sacrifice him to save herself. And apparently even Cindy is willing to sacrifice him too to save Casey. That has to hurt him a lot. No wonder he can't go to those hearings, and no wonder there's probably marriage troubles brewing (hence the "we're okay, there are no marriage troubles" statement from Cindy).