Their story is kinda sweet and romantic in a non-sentimental way tbh. Escaping slavery together and all that jazz. Can you turn Octavia more evil and let them stay together? (after fucking them both of course)
you mean the part where he treats her like his property?
That's not true. It's actually Octavia being SocJus trash, being triggered by wording of someone claiming another as "theirs". As much as Rogangar or whatever his name is is a cringily written edgetard straight from Tumblr, he actually makes a good point when you ask him about that thing in particular, saying that Octavia is only upset because she does not understand the difference between owning someone as property and owning their heart.
And that was actually a pretty sweet sentiment at the time, and really humanized him.
Overall, so far, I don't understand why he's even categorized as Chaotic Evil, other than a wish for some demented dichotomy between a Chaotic Good Half-Elf and a Chaotic Evil Half-Orc. So far, to me, he sounds Chaotic Neutral, quintessentially so; "I am free, fuck you, fuck everyone, I do as I wish, and what matters to me is my freedom, regardless of moral quandries". Single-minded focus on something fundamentally amoral (such as druid's focus on nature, a judge's dedication to law, or a bard's pursuit of the greatest song, stolen or not) is fundamentally Neutral. In Rorgangar or whatever's case, his focus seems to be on his own freedom.
His unwillingness or disinterest in the plight of other slaves isn't in itself evil, it's neutral. He'd be evil if he actually kept and promoted slavery, but afaik he does not. He just doesn't give a shit.