You sound brilliant OP, I really think you can do this.
I'm following your journey because I've lost and gained the same stone and a half for the last 3 years and it's getting me down. I've lost 3-4 stone using Slimming World in the past and actually enjoyed the process, but it always goes back on eventually.
Also, like you I have an event in about 12 months time that I want to feel better for. I great friend of mine got engaged recently, and her hen weekend and wedding will be on the cards in May and July next year. She is very slim and glamorous with equally slim and glamorous friends. I am the complete opposite and I don't want to stick out like a sore thumb!
At the moment I only want to loose a stone, but because of my yo-yoing for the last 3 years it may as well be a lot more - that's how much of an insurmountable task it feels.
I've decided to try a 'no diet' approach this time. I'm just eating three small meals a day and having an evening pudding (I've got a big sweet tooth). So today will be porridge for breakfast, a wrap for lunch and then chilli and rice for tea. Not counting calories, weighing or measuring - just cooking from scratch, packing in lots of veg and being sensible about portions. If I manage all of that in a day, I'm allowed a pudding.
My reason for taking this approach is that actually, the meals I eat are pretty good. The reason I'm fat is that I binge on crap nearly every day. I feel that if I could just get in control of the binging I'd make massive improvements to both my physical and mental health, even if weight loss is slow or marginal.
I quite like exercise and run at least twice a week and also do a HIIT session once a week. I can't run when my children are off school though, so that will be hindered quite a bit over the summer holidays.
I've been doing this for about 10 days and I've lost around 5lbs so far. I know a lot of that's water weight etc, but trying to use that to feel positive.
Sorry for the ramble, but it feels really good to articulate my train of thought!