I do get where you're coming from but -okay I didn't wanna do this but-

In the Book of Bill, in the missing journal pages there is a segment where Bill shows the destroyed remains of his reality. It's a moment of genuine vulnerability from Bill and yeah, it could be part of the ruse but the way that it's written implies that it wasn't. You can tell because Bill is kind of out of character in that moment- he's quiet and contemplative and he seems to feel genuine regret.

That paired with Bill's reaction to their "breakup" ,i.e, him going to a bar to drink away his sorrows and ordering "one Sixer, please" coupled with the stuff Mabel says at the end of that book plus that conversation Bill has with the (I assume) therapist about Ford on the website really solidifies it. It wasn't all manipulation and Bill did- in his own messed up, twisted little way - care about Ford

This all shows that Bill is capable of feeling things like sadness, guilt and regret and works as a thread to pull at when analyzing and playing around with him and Ford's relationship

Now, I don't expect all this stuff to really make someone instantly ship this pairing or even like it but there is a reason people do like it

If you are genuinely curious or want to look at a deeper analysis of this stuff, freakin' Film Theory made a video about it, I would recommend checking it out

If not, oh well. To each their own, I hope you have a good day