She has a fiance and she's happy with him...harsh as this may sound but that says it all. Could you really risk ruining that for her? I know it may seem like you love this woman but could it be that you are confusing your feelings a little? If she's the first woman you have been able to trust and talk to perhaps you think you like her more than you actually do? I really dont think you should try and break her and her fiance up, not only would it ruin your friendship but it's a really horrible thing to do. But if you just disappear and tell her you can no longer be friend you'll end up hurting her. It's really tricky but I think you need to tell her the truth, that you think you are having some feelings about her that you shouldnt be and that you know nothing can happen. Then let her decide what she wants to do. She may decide it is too risky to keep seeing you, but hopefully she will understand and try to help, talk to you etc, get you over her!! Who knows? Whatever you do though, i think you shld accept u cant be with this girl.