Hi I am engaed to a lovely man and due to get married in 2010 but I have started to think about an ex of mine am I going to marry my fiancé or not and what about my ex will things turn out to be fine

Being married and being single requries two different mindsets.

You're in the middle of 3 YEAR engagement? I think that would pretty much destroy me.

One warning, as long as you are still single, all random thoughts about other men have the chance to become reality. Even old feelings for exes...

Once you get married you have SWORN to ignore all those feelings for other men (which WILL still occur, you've just PROMISED to ignore them). Until then you are not safe from your single side because engaged or not, you ARE still single.

3 YEARS? Good luck, honey. I couldn't do it.

At least you aren't rushing to get married, and still have feelings for another. Make up your mind what you want, before you get married, or don't get married.
If you can't figure it out in 3 years, you never will.