Oliver Ward is nothing like the dudes Susan grew up with. Those guys love literature; Oliver loves getting his hands dirty. They love intelligent discussion; he loves getting down to the task at hand. They prefer Pepsi; he prefers Coke.
Okay, so that last one might not be true, but you get the picture. While Susan is definitely attracted to Oliver's nonconformist nature, the same traits that at first send her swooning end up driving her crazy over the course of their marriage.
In fact, Susan is attracted to Oliver in the first place because he's so different from everyone else she knows. He's ruggedly handsome in a way that sets him apart from literary pretty boys. He's straightforward and honest. And he's so masculine, which Susan can't help but swoon over. For example, Susan first falls in love with Oliver when he holds onto her ankle as she hangs over the edge of a waterfall—she describes it as "the very hand of the protective male" (1.5.5).
Susan starts hating these same qualities as soon as the honeymoon stage is over. First, Oliver's inconsistent work situation leaves him too broke to pay for her train fare, which offends her more than she'd ever admit. Then, we see Oliver's honest disposition become a liability in the shady world of big business. Finally, Oliver's masculine desire to care for his family goes a little overboard when he spends too much time working, leading Susan to believe "that his family must come second to his job" (8.3.10).
Oliver has a very consistent response to Susan's critiques: he shuts down. Susan tries to talk to him about her concerns, but he refuses to open up, and instead, he focuses even harder on work. Oliver also tends to turn to booze for relief, as Susan angrily learns one night in the canyon. Susan might go a little overboard in her response, but that doesn't change how lame it is that Oliver refuses to even discuss these issues with his wife.
This refusal is on display most prominently in the aftermath of Agnes' death. Although Oliver might have had suspicions about Susan and Frank's relationship before, he never expected things to end up the way they do. This sitch pretty much puts the final nail in Oliver and Susan's marriage, as Oliver starts ignoring Susan and "abandoning her in her grief and guilt" in the aftermath (8.7.85). Although Oliver never comes out and talks about his feelings following this tragedy, his actions speak louder than words ever could.
In fact, Oliver is so naturally introverted that we don't actually know much about his beliefs and opinions. While Susan wrote countless letters and books and drew even more pictures, Oliver "left no novels, stories or reminiscences to speak for him" (4.2.210). That's a bummer because his perspective would have been really enlightening. Instead, this practical-minded pioneer leaves tributes to his life in other ways: for example, he names a canal after Susan and a rose after Agnes.
Even if he can never be honest about his feelings toward Susan after her betrayal, we get the feeling that Oliver eventually makes peace with his traumatic past in his own quiet way.