After all, he comes by not keeping his fat yap shut honestly because it's one of the things he inherited from Elly. As this sequence indicated, Elly cannot be trusted to not say what's exactly on her mind because she thinks that tact and decorum equal deceit; while she might regret it later on, she always seems to find a means of turning things around on the people she inconveniences.
The reason that I mention this is that habit he has of running his fat yap and not being able to understand that sometimes, a lie is more moral than the truth came back to bite him on the ass. The incident in question when he couldn't keep his mouth shut about his living arrangements because of this stupid need he has to not shut up and his refusal to understand that he should maybe have lied about where Deanna lived so people wouldn't go creeping on him for leading her astray were reasons that he was a fool to to boast to Liz and to think that his family could be trusted to not pry into his own affairs. The end result of this is that the Pattersons still think that the Mira who would probably just have burst into bitter tears because she'll never be part of the big, fancy wedding her stupid bitch daughter refuses to admit is something she might maybe deserve is a monster. Also, the end result is that Liz still doesn't know about the weddings for show and for heart because Mike thinks that she can't be trusted to keep a secret he did a shitty job of keeping in the first place.