1) I think it is entirely normal to feel the way you do about your fiancees past. You won't be the first guy to feel like it and you certainly won't be the last. However, it is your problem, and I don't think the answer is telling her not to mention it. It's part of her past, it has helped to make her the person she is, and you need to accept it, not try to pretend it never happened. You need to realise that she is a person that has existed on this planet since before she knew you, and that she has a life of her own, just as you do. Being jealous over her past is both futile and arrogant, and she should not be in a position where she feels she can't mention it, because to do that is to deny part of herself.

2) Again, I can understand that you may feel insecure, that somehow your fiancee prefers the vibe to you, but ask yourself why, if the vibe is so good, that she bothers having sex with you at all. The answer, I imagine, is that you can provide plenty of things both sexually, and emotionally, that the toy cannot. Adding the toy, just heightens the experience even more, in the same way that you may find sex even more stimulating if she happens to be wearing a certain thing (or perhaps even if you were having sex while watching pornography or something). She loves you, is attracted to you and obviously has great sex with you, so I think your insecurities, while understandable, are completely unfounded. It's a battery powered object, so try to keep some perspective on it. Given the choice, I'm sure she'd pick you, but there's really no reason why she should choose. If you are concerned about being the best lover you can possibly be, the best way to become that is to accept your fiancee's vibrator and allow it to enhance her sexual experiences.

In both cases, I think you should (diplomatically) share your insecurities with her, but in a way that makes it clear that you are not blaming her for them, that you realise that it's your problem, but that you are working on dealing with it, so that she can be sensitive to the situation, without taking ownership of the problem.

__________________
"Time flies like an arrow -
Fruit flies like a banana"

M Y - N A U G H T Y - P I C T U R E S ! !