I feel like I'm in a minority then cause I don't think I would ever romance a companion that was like that unless maybe its with one of my insane PCs that would do the same. I don't know just the thing seems very close to making it an abusive relationship which I can't see how it would be fun at all.
Oh, no, you're in the majority. Rest assured. A yandere is an unhealthy relationship.
Of course, given the number of remarkably unhealthy companions Bioware throws at us, I've no doubt they could make it entertaining and even sympathetic. A yandere archetype is inherently obsessed, but the nature of the obsession is what can make them more interesting than a random creep.
One motivation for yandere is emotional dependence on the target. That sort of suicidal saving throw, where the yandere only finds hope and strength to move forward by pinning the hopes on the target because otherwise they'd have nothing. Dashing those hopes, however one sided, then becomes a basis for homicidal rage. If you understand that, than a yandere's character development could be emotional rehabilitation to the point at which they aren't so dependent. A character arc could thus mean helping them outgrow the yandere tendencies.
Alternatively, the yandere tendencies could be a subject of pity and victimization for the yandere itself. Imagine if the yandere was someone who was brainwashed and outright conditioned, against their will, to be like that: what comes off as offensive would be a form of pity as the person has no choice. Again, multiple ways to play it.