When you go to class, stuff everyone else (in a nice way of course). You are there for you!
There must be some motivation there for you to be going

just got to dig in deep and drag it out some more.
Beauty is in the eye of the beholder and all that. Easy to say I know. The bottom line is when you look in the mirror you don't like what you see and you want to do something about that and more importantly you want to do it for the right reasons, health and happiness
You leave the group with positivity, that's good. Motivation pulling out a bit more
Look at and address what happens between the WI's.
Step at a time, take little paces as they are easier to maintain and while you might see people striding ahead, they'll soon be lagging by the wayside while you plod along
What's in your cupboards? Time to take stock and get rid of the bad stuff.
Treats and Syns. Now they are fine but and it's a big but. Moderation and self control is the key.
I was always of the, if it's in the house i'll eat it. So for me to start with I would not have the Syn type treats about and when having them on plan would walk to the shop and get just what I needed. Freddo, Magic Elf, Buttons etc... and if my fix was part of a multipack i'd get the smallest one possible and then put it at the back of the cupboard with a big note on saying summat like 'Hey are you sure, look in the mirror'.
I've adjusted to being able to keep stocks around without binging, but even now it can take great effort and self control. Curse the bogof offers, just make it all cheap!
Being scared to loose weight for reasons given is understandable. I'd suggest trying to rationalise in your mind why to do it and not sabotage yourself. For example If you don't try it you'll never know, where as you will no nothing will change if you don't. View some of the other factors. Do you feel better eating well, sod the mirror. How do you feel about it inside? Looks aside how does it impact your health? So what if sometimes it goes up as well as down, we're looking at the long haul and a trend downwards.
I can guarentee that if you loose weight it will become noticeable, it may take a little time but it will happen. Your body density is a fairly fixed variable and so when you loose weight you will loose mass/size. Honestly.
Good luck, have a rant and use these boards for support. It's what they were designed for.