I'm thinking of telling my girlfriend she might as well turn her Fitstagram account into an OnlyFans if she keeps posting those pictures.
That doesn't seem nice. Do you have some reason behind this?
She has gained a lot of weight and is rather slutty on there.
It is wrong to be mean to your partner if you don't like what they are doing. You should be honest and talk to them about your concerns for their weight and what they post.
I'm going to try and fucking trust her. No one likes a fat bitch so it should be okay.
Trusting her is the right idea. Trying to tell her what to do would be bad for the relationship and it could lead to fights.