what's the chance of being able to date your roommate, and have them break up with their partner? Like you can get everybody else to break up except them, and I want my roommate, and I don't like sharing.
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Usually, you can't alter too much the scripted NPC stories; At least until you actually complete their "act".
You may try to force some "bugs" by using cheats and editing their likes, inclinations and such, so they dislike everything about the other one, but I suggest doing a hard save before you try anything.