Your feelings are valid, so I don’t understand the “just” in “I’m just feeling sensitive right now,” as if you’re trying to justify feelings you are absolutely entitled to. If this happens frequently, THAT is the reason you’re upset, not that you’re particularly sensitive. (Although you may be sensitive and that may exacerbate the problem, the main issue here isn’t that you are sensitive but that your fiancé is INsensitive.) This is a real problem because your very reasonable needs are not being met even when you express them. Your fiancé is not giving you the attention you want and deserve, and since it sounds like this is a pattern, you need to put your engagement on hold until this gets figured out. And if it doesn’t get figured out, don’t marry the guy. I mean, yeah, planning a honeymoon is fun — AND HE CAN’T EVEN GIVE HIS FULL ATTENTION TO THAT! — but the marriage is way, way more important than a honeymoon, and if your needs aren’t met NOW, before you’re even in the honeymoon phase, then, honey, this does not bode well for a satisfying and successful marriage.
So, what do you do? Pre-marriage counseling, stat. He needs to understand, with the help of a mediator, that you are unhappy. And you need to understand, if this is a cycle like you say it is, what triggers the cycle and how you can help him find less personally destructive ways to deal with the triggers. And if the trigger is related to his general feelings about you, a commitment to you, planning your future together, etc., then it’s time for some serious discussions about whether this relationship has a future at all, let alone a life-long future. Being newly engaged is a really special time, and if your fiancé can’t even carve out one night in a whole month to devote his attention solely to you, it makes me wonder whether he really wants to be with you. You should be wondering this too, and asking him, and seeking the help of a counselor to seek a genuine and authentic answer (and not just the answer your fiancé thinks you want to hear because he’s afraid of hurting you or afraid of being alone or of making an irreparable mistake…).
Yeah, this isn’t your place to say anything. And since your uncle isn’t hiding anything — these comments are on a public Facebook page, right? — surely your aunt already knows what’s going on. And what’s going on between them is really none of your business. Obviously, your uncle is dealing with some personal changes in his life, and what you ARE entitled to discuss with him is your relationship with him and your feelings about the change in it. You should tell him how hurt you were that he skipped your wedding, how you’ve always thought of him like a father figure, and how you’re sad that he failed to show up for you. You could even express concern about his well-being, but stay out of his marriage. You could tell him you’re worried about him, you hope he’s ok, you love him and miss him, and you hope he finds his way back into your life. You could ask if there’s anything you can do to support him. But telling his wife that you know – or think you know – that he’s having an affair? No. Not your story to tell.