As the W of a former MLCer, I can assure you that it's quite normal for them to become their polar opposites. Do you know how teenagers suddenly hate the parents that they loved to spend time with before, give up all their "childish" toys in favour of new pursuits, seek out new friends, experiment with fashion, drinking, drugs and new images, etc--well, that's exactly where your H is at.
As that oldest, responsible child, he was probably not allowed to experiment and rebel in normal teenaged ways, which means that he has "missing building blocks" to normal development. Now his father's suicide has triggered depression and MLC, and in the depths of that depression he's become once again the teenager who has no idea who he is or what path to follow. He HAS to go through this to grow up fully, and because his brain is currently wired like a, say, 14-year old, he is seeking out younger and different friends, experimenting with alcohol, etc. Remember that it's agonizingly painful and confusing for him to have lost his sense of self--that, in time, may help you to develop compassion for him.
In terms of your second question, I read the same information, and thought that it applied to my H. His mother could be abusive, harshly critical and unreasonable, and that's who he became for awhile. I'm not sure that your H is unconsciously trying to regain closeness to his dead father by reliving his life--it could also be that, although when he was younger he criticized his dad's behaviour ("I would never leave my family and take an OW"), now that he feels the self-hatred of depression he's thinking, "I'm no better than my father--look: the same things are happening to me." (MLCers feel like victims of circumstances.) This would just reinforce his feeling that he's helpless to resist the path he's on.
