I don't approve of mentioning the OW in the obit, but I can see where it came from.
The guy's family is obviously devastated by his suicide. Suicide hurts EVERYONE who knew the individual. This is someone they loved and he is dead. He is dead probably because of depression associated with his affair.
I think his family is trying to rewrite the history and not make the suicide about him being a sleaze. It is easier for them emotionally that way. They can just tell themselves he was clinically depressed. They don't have to say to themselves "we raised a shmuck who was stupid enough to cheat on a lovely successful wife and then blew his brains out when he realized how he f-ed up his life".