Hey guys. This is my first legitimate post about anything worthwhile. Let's get started, shall we?

Okay, so I promised my fiance that I'd tell her anything and everything intimate about me she wanted to know. What I've been doing, embarrassing secrets, how my day was, the usual. But I also console my friends all the time and must promise them not to tell anybody, not even her. This has put me in quite the predicament. If I break one promise, I uphold the other. And if I uphold the other promise, I break the first. This has caused tension between my fiance and I as well as my friends and I. I don't know what to do without violating somebodys trust somewhere, and I want all my friends and my love to be happy, but this is ruining my social life and relationship with them. What do I do to make everybody happy and not get lynched?

There are many ways to see trust. It really depends on what you really want.
Trust involves priority. There's no way you can keep everyone's 'trust' if you see it in a black and white 'I can't tell anyone about anything!' way. If you trust your fiance as much as yourself, then shouldn't your trust in her be prioritised above your friends' trust in you?
I think it's unrealistic for your friends to expect that you should keep things from your fiance for their benefit, especially harmless stuff like this. You don't have to always be a yes man you know? If your friend asks you to promise not to tell anybody, tell them that you have a duty of respect towards your fiance in being accountable to her in what you do.
If your fiance is bugging you to give them unnecessary details that your friends would really not want them to know - and if you don't trust her enough to keep this between the two of you, then I suppose you could ask her to respect your duty of confidentiality to your friend. But in my honest opinion, almost married/married people should be able to share everything with each other. After marriage, you're practically one soul, aren't you? I know it's idealistic, but to me that's part of the point of marriage. After marriage, you and the other person become 'one' in many aspects.
That said, I can understand that you are a honest and kind person trying to not offend or hurt anyone. This is hard for you, but maybe if you speak up a bit you can form some sort of compromise. You don't have to tell your fiance 'nothing' when she asks you what you have been doing, right? You can say something like 'I was comforting a friend who would rather not be named, I know you understand.'
It's about working out the boundaries in emotional intimacy between yourself and her. If she is comfortable with telling you about all her friends' problems, then maybe she expects the same from you. However if she isn't, then you can gently inform her that you are similar to her in this aspect.
In the end though, you'll never make everyone happy. Focus on what is most important to you. Or rather, who. And just live the best you can. If you're always trying to make everyone happy, you'll lose sight of what is truly beautiful.

That was inspirational. Thank you. I'll try and help that some. I appreciate it, really.

A promise NOT to tell a secret is higher priority than a promise TO tell secrets. Explain to her that since they tecnically are not YOUR secrets you can't tell them to her. Explain that although you won't keep things from her, if someone trusts you with their secret you have an obligation to keep it from EVERYONE ELSE, even her, unless the person who the secret belongs to gives their permission.

"about ME" golden words right there. Are your friend's secrets "about me"? No. Therefor she cannot force you to tell them.

Yea there is no reason for you to have to tell your friends secrets to your fiance, that has nothing to do with your secrets. Try the practice of only saying what you have to, nothing more, nothing less. You'll get into fewer predicaments that way.