What we didn't look at, however, was the impact his actions had on those at whom they were directed---consciously or unconsciously. Both Steve's physical and psychological presence, even from the very beginning, created a certain level of instability that continued to undermine Shane and Oliver's relationship at different phases.
It wasn't until Higher Ground, however, that both Steve's existence played a truly pivotal and powerful role.
What Steve did in Higher Ground was expose Shane and Oliver's weakest point---their unspoken feelings for each other. Unable to discuss or regroup, they became restricted to what could be said covertly, and in a short amount of time. Shane's references to Gabe and Hattie were meant just as much for her and Oliver as for the separated couple. It was her way of "sending [Oliver] a message" before she had to leave him behind. In the urgency of the moment, and the realization their communication ties were about to be severed indefinitely, it's not hard to see how that indirect message might have been lost as time passed. With so much left to be said between them, the sudden separation left a huge void that only their hope and faith in each other could bridge for the time being.
A Hard Lobby
Once again, their sense of security is set into chaos because of Steve's actions, but in this case they end up at war with each other. Oliver's insecurity, which has behind it the knowledge that Shane's skills are no longer required, battles Shane's hard sell that all is not as it appears, ignorant of the circumstances thanks to Steve. What might have seemed an insignificant text in any other circumstance becomes akin to a bomb going off. But this time it causes Oliver to take additional action by requesting the return of his pen. Where Shane was sure that "she knew" of Oliver's feelings for her, this request threw that into question on her end.
Shane could have continued to press Oliver about "why [he] moved [her] desk" and likely gotten him to "it was hard to look at" without mention of Steve, but when she asserted "Steve says you don't really say what you mean," Oliver's continued inability to do so as Shane pressed for more transparency only served to reaffirm Steve's accusation. Frustrated, Oliver turns a bit on Shane, suggesting "[her] intentions and [his] were not in concert." This, of course, sends Shane into an emotional spiral as she attempts to prove him wrong.
Insecurity begets insecurity until Oliver has the courage to do what needs to be done to eliminate void that left them so vulnerable all those months ago. By kissing Shane, Oliver makes a move to restore Shane's security regarding his feelings for her, as Shane relaying the content of her letters has done for him. The decisive act goes a long way in repairing the breach and restoring their faith in each other, and hope for their future, in a more permanent, indisputable way.