Hi OP, I've spent most of my adult life the same sadly. 10 years ago I was at my slimmest which was still 13 stone odd which is where everyone else on weight loss threads seems to be starting from & it's my goal!
I'm 43 & need to realise that it's a full time job & rather than going on diets, I can occasionally have a day or 2 off a healthy diet instead.
However, I have managed to lose just under 2 stone since the 4th Jan this year. I started at 18 stone 9lb, which I was so ashamed of as I'd lost 1.5 stone just last year near the start of Covid. like pp says, I started with achievable goals, doing 10k steps a day & no alcohol in Jan. I then started logging calories on mfp.
I've been successful with slimming world in the past but I really didn't want to get back into it as feel resentful being back on that environment, (even though it's clearly my own fault that I regained weight).
I don't know why I've stuck at it this time, (so far). I built myself up to in while I was eating & drinking my way through December. Lockdown maybe helped as I said to myself, do 6 weeks of a prison sentence & take it from there. I knew I was going to be miserable whether eating & drinking or not & didn't want to hate myself more for failing at the end of lockdown. Losing a stone in Jan gave me such a massive boost to keep going. I have been thinking that I will set up a reminder on the 1st of every month to weigh myself & have a trigger weight where action must be taken!
I find it difficult not having support IRL but have joined a few of the threads in the weight loss topic & that really helps. I haven't really started doing any exercise yet, will try to start something soon but the 10k steps is great if you've a Fitbit or similar as it's easy to monitor and my inner child adores seeing the fireworks on screen when I hit my target! 😂
I hope you find something that works for you & you find some support to help you work through it!