There is a lot of valid responses on the focus of it is not in your control to fix. All of which I fully agree with. It's placing an expectation on you, which you simply don't have the power to fulfill (and I personally see a grain of sexism in there...wives/mommies are always seen as the "fixers").
What I've had more experience with ..even with a short, non marital relationship.. is the level of dishonesty in what REALLY has gone on. Most of the regulars here will emphatically tell you that the alcoholic SHIFTS BLAME as part of the denial process. Using the partner as a scapegoat. My x and I had several blowups, all of which were without others present to witness. Within a few days, his buddies clearly were distant, hostile and with unspoken criticism, towards me. If the x wanted to cover his part, he was easily able to do so, at my expense. He might even go as far later, to grudgingly admit to being responsible for something.. but the damage was done, in terms of what he already had told others.
Your partner may well be telling the friend that he is doing GREAT.. but that isn't necessarily true, and your friend is likely in a position that he accepts that, without knowing the facts.