And I also don't buy anything about him feeling bullied or tormented into standing by his bigger (or smaller?) blood brother. To me, the simplest, most plausible explanation is that they are more alike than dissimilar. Not just in looks, but in values and upbringing and survival skills--by that, I mean, what they will do to make things work, to make things okay, to cover up what's necessary, and to acquire success.
Thanks to the sleuthy sleuths here, we know it is clear that these guys are incredibly intertwined and always have been. (MS was engaged to CWW's wife's aunt at some point? I am getting that right?)
The percentage of their lives that they spent as besties dwarfs the time that MS has known TS. I think, like old war buddies, these guys were in the trenches together and can understand each other better than anyone else in the world--only, these were the trenches of badness--RB, for starters, and meth, what else?--and they still accepted each other nonetheless. As whacked as it is, that is true friendship. "I'll be there..."
Two low lives grew up together and supported each other. One was able to put on charades to marry someone who could elevate his status in the world and probably wouldn't accept the REAL MS. I suggest that in his life with TS he was living a lie and riding coattails to success, but in his life with CWW, he could let his "hair" down.