Liz, mine did virtually the same thing when he found out his best friend had cancer. He didn't mention it for a few weeks then simply said so&so had surgery a week ago and is starting chemo in a week. He didn't go visit him upon the news, nor visit him in the hospital, nor after. The relationship was different than with your AH's friend, and I believe mine didn't mention it to anybody in his family because then it would have taken away his "his" time drinking...plus his best friend was also his best hangout/drinking buddy and he probably saw that drinking relationship being out the door since his friend wasn't going to be drinking like that anymore.
Regarding being accused of cheating...one time my XA called some of his friends and family (while in a 4 day drunken raging stupor) and told them a bald face lie, that he knew was a lie, that he found out I had been "dating one of my guy friends"....then later he said that nobody had been on the other end of his calls.
I've always figured 100% of the time in situations I'm aware of that the accuser is the one that's been unfaithful.
Once mine realized I would not have sex when he was drunk, he would try to go there at the midpoint of drinking for "I'm-not-stumbling-drunk-yet-but-I-intend-to-be-in-10-more-minutes-so-why-can't-we-do-it" sex. And then carry on with accusations that there must be a reason I wouldn't.