It's bizarre how much abuse both Fraser and his fiancee are receiving for just moving on from a friendship that happened 10-15 years ago! Is the ego this fragile that the only way to accept a friend dropping contact is (i) his fiancee is controlling (ii) he was in love with you (iii) he's a bad/weak person.
Can it really not just be the reason most people in their 30s are not in touch with old friends - they don't have the time balancing work, relationships, kids etc and choose to prioritise new friends and relationships that are more fulfilling for that stage of life. How many men actually stay in touch with close uni friends of any sex once they're in their 30s and 40s - if OP were a man, people would just accept it as the cycle of life. It's only because OP is a woman, his fiancee needs to have been involved in him losing touch. OP herself lost touch with everyone in their uni gang of 15 people except Emma and Fraser - it's just life.
Men just approach friendship differently, they don't attach the deep emotional connection and meaning to it that women do past a certain age. And once they meet their partners who fulfil any emotional needs, they just want low effort friendships that don't need as much contact or time or emotional energy. That's why male friends can say in touch for months with just memes on whatsapp, meet up for drinks and pick up the friendship with no drama. Then go back to memes. Whereas a female friend like OP would be annoyed they hadn't met up more, spoken more, had more in-depth convos, been on trips together etc just adding more emotional complexity. Most people don't have the bandwidth for it once older especially if they have other close friends as well.
This possessiveness of friendship - that it must last a lifetime with the same intensity is why some friendships get dropped. Because no one wants the guilt tripping of a friend who expects a similar level of contact, and for everything to be unchanged, not accounting for how their friend's life has evolved. Work becomes all consuming, people meet other friends in a similar life stage, couples make couple friends, people buy houses and think about children, they develop new hobbies, and they fall in love - in summary they change and want people around who know and support them as they are, not as they were. And people can sense when an old friend is not supportive of change, particularly if the friend's life hasn't evolved in the same way.
Also bizarre that everyone thinks the only reason Emma is friends with him is because (i) she brown nosed the fiancee (ii) the fiancee can gatekeep their friendship. Can it really not be the most obvious thing that after all these years Emma realised the fiancee wasn't some villain and is actually a nice person, and they have common interests and get on well. And her friendship is now more with the fiancee than Frasier as a result. She'd have to downplay this for OP who would no doubt see this as a betrayal because OP still sees the fiancee as the reason Frasier dropped her.
OP, I assume you must be mid 30s if 15 years ago you were at uni? I assume you don't have a relationship where your emotional needs are met, or haven't made any new friends who fill the emotional gap Frasier once did and Emma doesn't offer what he did. And that's where you should focus your energy, finding your person. Frasier just met his person - the one he shares finances with, discusses his problems and deepest feelings with, will lean on when he gets sick or redundant or has elderly parents, goes on trips with, may have children with and has built a whole life with that needs way more commitment/time than a friendship. Unless he has no other friends, it doesn't make him or his fiancee bad people for dropping you or prioritising their relationship over you. Hurtful for sure, but it's been years now so enough time to fill the gaps he left. If you haven't found a single living soul who replaces his friendship in 15 years, I would gently suggest it was more than a friendship for you - maybe not romantically, but you certainly liked being his priority and enjoying some of the benefits of a relationship.
I don't know if Emma knows how upset you still are as she may have assumed you've moved on. Be honest with her, and have her stay elsewhere. I don't think you're worried about Emma's reaction tbh, I think you're just stinging from the realisation that Frasier has really moved on, and the fiancee isn't just a blip. You cannot be invited to a wedding where you don't like the bride - it's just common sense. The wedding isn't a party, it's a declaration of their love and commitment to each other so only people who support them both are invited. So please don't let Emma ask them to invite you, that would be humiliating for you.
I hope you find someone with all the things you liked in Frasier - but this time as the gf and the priority. That's how you will move on and maybe also understand why he prioritised his relationship over you.