Well, probably not. But. There's a "but." 

SS, now in his late 30s, moved far away from BM last year. He has always been under extreme pressure from BM and SD to stay close by, to be part of what I call their little dysfunctional cult. As awful as SS can be, I've handed it to him that he has had short periods of resistance, and I know it hasn't been easy for him. 

SS has been dating a woman and told DH that he believes they will get married. 

When SS was in high school, BM said that she had already "picked out" who he was going to marry. SS has not had much luck with dating, and I've always known that it is in part related to his domineering, intrusive mother, and likely also related to his obnoxiousness, which worsened over the years. At SD's wedding, we met one woman he seemed serious about. She was seated next to me at the reception (therefore, you know her status...ha!). We really liked her. Within two weeks of the wedding, they had split. The reason, SS told DH, was that the girlfriend was a bit overweight and he feared she would regain more weight and be a fat person. Note: BM is obsessed with weight, hardly eats, and pushed SD into what I have long believed to be an eating disorder (SD's weight fluctuates wildly; when she was younger she was a food-hider). We know where the pressure came from. My gut told me that BM had been embarrassed of SS's GF at the wedding. . . because she was mildly overweight.  

We have known that BM has never approved of any woman SS has dated--and I can imagine that sane GFs probably wanted to run the other way after meeting BM. SS's dating history is abysmal. 

So what now? I can't imagine a big family wedding (thank the stars). I'm assuming SS, if he marries, will stay permanently 1000+ miles away from BM. So, perhaps by the time he hits 40, he will have gained real independence for the first time in his life. Or maybe I'm delusional and still have not put down the hopium pipe. 

SS has been a jerk in many ways. Still, I hope this works out for him and he finds peace. And wishing strength to the woman!