Scared my dress won't fit

Hi there. I think many of us worry about this so firstly, know that you are not alone. I'm not an expert, but have a few ideas...
It might help for you to buddy up with someone (e.g. your mum or a bridesmaid who also wants to lose some weight before the day) so you can support each other. I'd also definitely speak to your fiancé, especially if you live with them. They will always think you are beautiful as you are of course, but getting their support is really helpful. For example, my fiancé used to always split the food we cook 50/50 when he plates up - he is doing it because he is kind and doesn't want me to go without, but forgetting that women need 500 fewer calories than men per day so my portion should actually be about three quarters of the size of his. We also discuss our meals a lot, so we can work out something that works for both of us (e.g. he might have mash with potatoes, I have it with cauliflower). That way, you are still having the "same meal" and can eat together, which is much less miserable than him sitting there eating something amazing while you tuck into a green salad with no dressing!
Also, it might sound bonkers, but when I'm feeling demotivated to go to the gym or want to eat a load of sugar, I close my eyes for a minute and visualise myself the day - in my head, I am healthy, confident, full of energy and have glowing skin and that helps to get me going. Sleep is so important. Not just because our body works better if you are getting enough sleep, but also because when you are tired, the desire to lounge about eating snacks is much stronger as you want to "reward" yourself for getting through a tough day. Finally, find a "treat" that isn't food related. We all tend to fall into the trap of "I've been to the gym/been good all week so I can treat myself to a massive dominos etc." Try and switch this to something else, maybe "reward" yourself with a long bath, a face mask, doing your nails, that book you've always wanted to read - something for you, that isn't unhealthy food.

I've recently been able to lose a reasonable amount of weight using Noom. Honestly a lot of what they teach though follows the great advice that Mrswdesig has posted above. It's a lot of visualisation, rewards that aren't food and drink, sleep, looking after your wellbeing and considering calories vs. food weight (100g salad has fewer calories than 100g crisps but it fills the same space in your stomach). It does genuinely change your relationship with food and is quite reasonably priced for the lasting change I feel that has made on my habits.

Don't beat yourself up about motivation to exercise- losing weight is mostly to do with diet but exercise helps with fitness. Think instead more about all day movement. Go for a walk with a podcast/music/audiobook when you're feeling unmotivated to go to the gym. It's time you've already carved out for fitness but as long as you're moving instead of not moving that's the most important thing. Also, exercise doesn't have to be confined to the gym or specific times. Whack some music on loud and have a dance in your lunch break- it'll get your heart rate going and boost your mood.

The biggest thing that helped me when I was losing weight was meal planning, specifically evening meals for me and FH. I used meal delivery services (Gousto is the fave in our household but we've also used Hello Fresh in the past). You can choose meals based on the calorie content and then you're not having to worry about portion sizes and counting your calories and you already have a reliable guide as to what you're eating.

You'll absolutely smash this and I'm sure you'll look stunning in your dress!