BPDs aren't users per se. The using isn't the end goal, it's a byproduct. They will utilise it to get what they want, but what they want is usually not to be abandoned, to be loved, catered to, taken care of emotionally, be fulfilled. If they can have you without opening up and have control over you, that's all the better. But a lot of them (intentionally or unintentionally) put in a lot of actual emotion into their relationships and develop codependency. Leaving someone they are "using" is just not BPD modus operandi, and they can feel both like they are unable to control their victim, and feel the repercussions of this codependency in the form of anxiety or other negative emotions. As destructive as they tend to be, they genuinely do oftentimes believe they love the person and they try to act accordingly and will even experience these strong emotions of love and display them lavishly.
TL;DR Wifey is a fatass fatty fat grifting uggo user narc because BPDs at least try to pretend they love you convincingly.