This brief intro is just to maybe help explain why supporting someone who is on a diet is becoming so exhausting.
I had very triggering things said to me as a young girl. I started to develop very poor (non existant/distorted) self esteem. I am 18 now and it still affects me very much. I have an awful relationship with food and eating.

Over the past 6 months most noticeably, I am finding it increasingly hard to support my mum with her weight loss.

For the past 3 years or so, she has been trying to lose quite a large amount of weight she has gained. At first I found it really great that she wanted to get more healthy foods in the house, do more exercise etc.

I helped her come up with meal ideas and motivated her to get more exercise by going on walks with her and just trying to educate her a bit more about food contents.
She had lost roughly 25lbs. That winter however her 'diet' seemed to slowly come undone and she went back to eating bad foods and less exercise. I'm not sure why I didn't do more to help her stay on track, but being at college I guess I was just preoccupied.

Since her gaining those 25lbs back, she has been on lots of little diets that never last longer than 2 weeks. It really feels out of my control to get her to lose weight. She has asked for my support lately, but I'm finding it very frustrating to give her it. I have been snappy with her, and slightly blunt.
I can't understand why with so much help from me, she struggles so much, when I do everything, especially regarding my food, by myself.

There have also been times when if I have been snappy about something she's eaten, I've felt so guilty afterwards. thinking like "What if I made her feel like I was made to feel?"

Maybe the main problem is that to her, dieting isn't so important. It is a huge part of my life however. I really do try and help, but I also get no help in return

I love my mum a lot, but our relationship is very unstable atm.

I'm hoping someone can understand how I am feeling. I feel incredibly selfish thinking about this :[
Sorry this turned into such a huge post

It sounds like you would really like to help your mother, but in the end it isn't your hand that puts the food in her mouth. Helping her understand what she needs to do to lose weight is great, but she needs to do it herself. I just think weight loss is a very personal journey and you can't succeed or make it last if the only way you do it is if someone is pulling you along. Maybe she can look into some external support program if that's how she wants to do it?

She can't lean on you for this. She has to do it. SHE has to choose it. It sounds like you do some of the parenting of her instead of the other way around. You are too close to the situation to be her coach. Help find her a support group and maybe go with her to the first meeting. There are some non-profit groups like TOPS she could join to get the support she needs.

You are not her only solution. You need to break away from that idea for BOTH of your sakes. She has ownership of her life and choices and you have to own yours. In your case, it may mean finding a way to break free of past hurts and developing SELF esteem and confidence. She can't give that to you either (not that you're asking her to) but each of you have your own journey.

I wish you every success.

My mother never found out what had been said to me until I was about 16. My parents are divorced and it was my dads family who said this.
Obviously she said she didn't like what they had said (or so she said), but soon after it was just that I need to get over it. Great advice but useless when you can't seem to

I don't get why she can't take her own advice and just get on with it, if it's that easy?

I am a 'normal' weight, but always trying to get down further, and then gaining it back and it just repeats. But she has seen first hand how worked up and upset I get over it, but I'm supposed to care about her weight problems, when she doesn't mine?

I hate feeling this way, I'm actually a very caring person 8-)