Honestly, I think the fiancee and the best friend might end up together.
Tomoe who thinks Ayano is definitely going way too far for a woman she barely knows but who ultimately respects Ayano's drive and wants the best for her, and the fiancee who just revealed to her that he's really only playing along to get Ayano to understand that this is a futile endeavor so she can become his wife without issue?
Also let's not forget Tomoe has been jealous of Tsubaki all this time, because she wants to be the one supporting Ayano, she's acted the way she has so far because she doesn't really want for Ayano to help Tsubaki, because if Ayano does, then Tsubaki not Tomoe will become the most important person to Ayano.
So I'll be honest, I do not think Tomoe would want anything to do with the fiance, I think he's here to provide a mirror through which she can see how her love will not lead to a fundamentally different result than his disdain. So as to spur her into action and actually do what's best for Ayano rather than placating her own feelings by supporting her endeavors only on the premise that she's likely to fail.