His arms constantly slide over her shoulder or around her waist, his touch an inextricable part of her day. He traces her body just as much at work as he does after hours, though of course it manifests quite differently depending on the setting. The running theory is that he wants to scare off the competition. He's possessive, marking his territory, the message as clear as when he insists she's "married to science." That may well be partially true, but whole truth is more often than not complex and multi-faceted.
Cave Johnson is a man of words. As a proud and confident CEO, he loves to hear himself talk, and it's a talent as much as a hobby for him. His fat mouth has gotten him in trouble countless times, but his silver tongue always pries him free. He always knows just what to say when the government came snooping around. He always knows just what to say to make her clutch the nearest steady surface for support, his charm taking her by surprise even after years of seduction.
There are some words, though, that don't come out as easily as others. For all his skill in flirting, his speech is hindered when he looks over at her, seeing how her hair drops into her eyes without her even noticing as she pores over some important document. He cannot articulate his thoughts on the warmth that floods into him as he lays next to her in bed, watching her steady breathing in sleep. There is no way to verbally express the level of comfort that her mere presence brings. There is no way to explain the feeling that he holds, without even trying, for her.
Well, there is a way. It's just that he can't say it.
He reaches to tuck a lock of hair behind her ear, one she hadn't even noticed was blocking her view, and she smiles to herself. There are some things he'll never say, but he always ensures that she knows.