If you want to get married though, you should get married. Girls don't need to try and kill themselves to fit into a dress when they buy the size they are, not the size that they want to be; us girls do that to ourselves. With wedding dresses it's a little different too since you order the size based on your biggest measurement and then get it altered to fit everywhere.
If you wait, then I think you have the stress of planning on top of the stress of maintaining. I don't think the stress of wedding planning dissipates because you're fit, since now you're potentially Super busy and you have your shower, bachelorette party, food tastings, cake tastings, engagement party all of which could easily throw off your diet & exercise. I think it's admirable that you want to be healthy & fit, but I don't think it needs to come at the sacrifice of your wedding. What if you didn't hit your goal next year? How long do you continue to put off your wedding then? If you take a year to plan your wedding, you could hit your goal of 50 lbs or close to it. I suggest picking a date and then that's the time you have to do what you can in terms of weight loss. Your fiance loves you just as you are and wants to be with you now or 50 lbs lighter. Good Luck!! :)