I have talked to a few friends (who know him) and they think that he is imploding, having a massive crisis. He’s very thin and looks ill. he’s not sleeping and he’s very run down.
I've been on MN a long time, OP.
Over those years, I've read many a thread where a poster is concerned about a change in her husband and os worried about a mental health crisis.
Everyone whose been through it posts, it's an affair. The OP is sure it isn't.
I haven't read a single thread where it turned out that the husband was truly having a mental breakdown. Because no one has a mental breakdown through not being paid enough attention when their spouse has been bereaved. No one.
The change in him is down to the guilt he feels and, more than that, his fear of how he will be perceived by others for both leaving you when you're bereaved and having an affair.
I'm not saying this to be cruel.
But DO NOT trust him now. He is NOT your friend. He DOES NOT have your best interests at heart. He will undoubtedly still care for you if he's not being actively cruel but his priority now is himself. Protecting his assets and maintaining his image. He is not your friend.