Sadly, I really think the arc of Logan and Veronica's relationship IS leading up to Logan cheating on her by the end of the first arc. Although, I would be actually thrilled if he WASN'T, but Veronica THOUGHT he was and dumped him. Then Logan could basically be like, "this is bs" and they don't turn to hating each other again (ala S2), but there is bitterness. Then the second arc would have her battling her supposed "proof" with wanting to believe Logan, all the while Piz is there all along as temptation by being the nice guy. And then have by the end of the season, we have Veronica realize that she is going to just trust Logan and go to him and tell him, she's decided to just believe him because she does love him and wants to be with him. THEN have proof drop into her lap that he did NOT cheat and that would make her realize she was right to trust him.
Yeah, I know, it'd never happen, but I could so live with a break-up and even understand the role of Piz in the season. And it would be about both of their issues.