Since he says other people in his family understand his behavior, then maybe you can ask some of them.

The thought that pops into my head is that he is actually feeling guilty about something he did or didn't do while his mom was alive. Just saying--I can't say for sure, so don't take this completely as the truth, but maybe something to consider....

Or reaction formation? He really has a lot of anger toward her?

I know many men love their moms dearly, but from what you say, he is really reacting strongly to her death.

Yeah, I suggest speaking to his relatives about it, but maybe just telling them what he is doing in not a negative way. Maybe even saying, "(Jim) really must have been close to his mom...." And maybe see if they comment on that.

Other folks, what do you think?