Doug had inherited his money from his dead wife, yes.
The colder Holden mostly sustains while Marland is alive. After Martha Byrne returns, the traces are still there, but there's more and more focus on him wanting to win Lily back and proving Damian is a criminal. There's also the story of him taking Aaron back from Iva, a story which angered me a great deal at the time, because a) I'm petty and I always thought Holden was a smug dullard while Iva was one of my favorites and b) he dumped Aaron off on Emma all the time to chase Lily and then to start dating a woman while pining for Lily. He spent more time caring for her son (who was deaf) than he did spending time with his son. There was finally a scene where Emma told him he was a deadbeat, essentially, and to raise his child. Not that long after this, Holden finally realized he needed to move on, and left Oakdale with Aaron. He was off the show for about two years, until early 1997, and when he came back (minus Aaron, who was taken in by Julie - bad writing as Julie was not capable of raising a child), he became the Holden you described.
The main reason John left Lucinda is because of her lies and control issues, some big ones involving his last long lost son, Duke (not sure how much detail you really want as I'm sure you will be watching them someday). He and Lucinda divorced in 1990 but he still remained close to her.