NC for this post but am a fairly old hat.
BF has been divorced for about 4 years. He continued to live with his wife for about a year after they split until she got her own place. She's now engaged to someone else. He's quite vague about when it all happened but I've met her and they are definitely divorced. I've met his family, been on holiday with his kids and parents and no suspicions over him still being married incase any one suggests that.
One thing I do find really weird though is that he says he didn't even read the divorce papers, he just signed them. I say bullshit. His wife filed for divorce and he just went along with whatever she wanted. Why would he either lie about not reading them or if he's not lying why on earth would someone not read why their wife was divorcing them? It makes no sense to me and I don't see a reason to lie.