My girlfriend rejects my help and support?

My girlfriend has a bigger stomach than other girls, and while it isn't a game changer for me and I dont rlly have a preference about it she feels fat a lot and im trying my best to help her.

In all of our almost 5 months relationship I've been trying my hardest to help her and even suggested to do a diet together so she won't feel alone in this when she started her diet

Now she told me right before she left to her friend that she won't fit into a pair of pants she did a month ago and as a pretty decent boyfriend I did my best to help and clear things out and telling her what I think about it and stuff, and in the end I tried doing another diet with her.

she refused and said itll make her feel bad that im doing her "because of her" and that she will do it alone, so I said what I think any reasonable man would say "then ill be here by your side and support you"

she refused my support in what felt rlly cold.

"I dont need you or anybody's support"

and then she left to her friend and I was there looking at the message and I still wonder if there's something I did wrong. or was it something I said?

Guys (or girls), Did I do something wrong? or was there something else I needed to do?

My girlfriend rejects my help and support?
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