Well, I think it would've been shitty if she had just given up on her current bf or handwaved it with "oh I never actually loved him anyway." like some stories do. Yeah, she probably has some feelings still, but truth of the matter is that Wakana was just too late--she's already committed now (in an assumedly happy, mutually requited relationship). Girl's just bi yknow?
(And yea, she could've been the one to take initiative back then--but that's not more her fault than it is Wakana.)
Also, I don't remember if there's been signs of her having feelings for Wakana; I might just have to reread it. But I kinda hope that Yuina was just messing around. It just feels kinda... cheap? when the story goes "oh, your best friend was the one destined for you all along!"
'Cause then, as others have mentioned, I don't see the point in this whole extra arc for anything else than some extra drama. Just let the girl find someone else? There's plenty of fish out in the sea.