I think 'bittersweet' would be more if there was something to be sad about in the mix - which you could argue there is since alternate versions of both of them had to die before these two wound up together, but I don't think that was what you were getting at? But it does put a different spin on this scene when you know what they've gone through to get to it - and the epilogues are all about showing things working out for them afterwards. (Well, that and resolving those last few little details that still needed resolving.)