This isn't true, to romance the roommate continue with the dares their partner gives and eventually the roommate will have one of their own that is more extreme - after which you get an option to be their submissive along with their partner
Getting into a relationship with the roommate is only possible through the roommate's partner at the moment. Keep in mind I've only done this storyline once months ago so my memory is fuzzy, but basically:
Start out the partner's storyline by eavesdropping on the two of them having sex (randomly happens waking up in the morning, more likely to happen on the weekend). Eventually the partner will confront you about it, then start giving you dares.
Keep doing the partner's dares, don't fail a single one! Eventually there will be a sock on the doorknob when you go to your dorm room. Go in anyway and interrupt your roommate. About a week later the partner will show up and ask if you caught them doing anything, tell the truth. The partner will punish your roommate in a way that puts you in a dom or sub position.
Another week or 2 after that the partner comes into your dorm again and gives you the chance to be in a throuple with them and your roommate, either as submissive to both of them or you and the partner dom over your roommate.
Oddly enough getting into a "relationship" with the roommate doesn't seem to fix their negative opinion of you, and in my game they were my dom but fucking hated me and broke up with me a few days later. Idk if that's intentional game design or just an oversight though.
So, getting into a relationship with anyone doesn't immediately change their opinion of you at all. That's intended behavior. However, having positive interactions with them will slowly increase their opinion of you. I've actually had what were originally hatefuck characters eventually get up to max friendship after a while. The difficulty is that if their opinion of you is low enough, the opportunities for negative interactions are far more frequent than the opportunities for positive interactions (at least as far as random events).