I think she's intended to be problematic and uncomfortable to deal with because of the new dynamic -- the ending of 12 kind of grounds the "out of the loop" feeling of the MC in context. I hope the story picks up from here and allows for a resolution that brings you and her together. The storyline has presented them as the couple to root for from day one, and that makes sense in-story, so this is hopefully a lover's trial thing that resolves that way.
Heidi, after all this time, is still kind of a cipher to me, and I'm fine with her as a fling of sorts. Then again, during that last date thing I was more focused on getting laid, so heh.
As I always say, I wouldn't say no to a threesome (MC and Amanda, with Kathy) as well on the way, because that girl is hotttt. That first scene with her, with the beads of water on the skin... sweet damn.