It's pretty simple, pet. You think it's a good idea to wear corsets day in day out despite the potential health risks. Your parents don't. (Your dad might not be so vocal on the issue, but I can guarantee your mum is bending his ear about the subject every night and he's siding with her.)
You're not going to change their mind. Neither are they.
Having tried and failed to get you to see some sense, your parents are now shifting the blame onto your boyfriend. Might not be the best thing to do, but what else
can they do? You've point blank refused to see their point of view, so hey, if they can't control their daughter, must be some sort of bad influence. Who's a key figure in her life right now, outside of the family? The boyfriend. Yup, it's got to be the boyfriend. All his fault. Obviously.
If you don't compromise about the corset issue, nothing is going to get any better. I appreciate the above might sound a bit harsh, but as an outsider looking in, it's the honest truth. Your parents are wrong to make your boyfriend the scapegoat, but you've pushed them to it. Try to understand their point of view, and offer to wear corsets less often. (I'd say stop altogether, but I know that's not going to happen.

)
Sympathy hugs for feeling down, though.
