Wow, I reread this, and please don't take this any of this as me being down on you at all for being 'boyfriend girlfriend etc.'. No judgement here, just suggestions!. I'm glad I looked before I went to bed! So please, just read, and understand what my sister went through (and I haven't listed any of the grief she went through and she remains single to this day, and isn't interested in dating, etc and is essentially a changed person).
end edit:
Keep calm and carry on.
My mother didn't talk to me for a week when I told her I was moving back to my college town. Took my Dad telling me that for me to notice though.
In the end, she bought me a down comforter (thankfully she did, because I lived in an unheated attic for a month!) before I left.
My parents did this to my sister for YEARS. Not saying this will happen to you, but just be aware, you might be doing the 'adult' thing and doing the 'proper' thing in the midst of histrionics just like this for as long as you want to 'save money'.
I'd clear up your situation with your 'boyfriend'. Most people think they are saving up for a wedding, but get real, if you are going to get in debt for a wedding but not school, it's a little backwards. If you guys are not just in love, but marriage material, you may just want to tie the knot!
What to do about your parents? You can't do a darn thing. No one can make them grow up and expand their consciousness to another family (your brother isn't married yet?)
Don't expect things to change. Just because you get married, doesn't mean they will change their tune.
You ARE their baby. For some parents, that status continues well into adulthood. So, bear that in mind too.
Be clear, be sincere, express empathy, but you made your decision a year or more in advance, and now she's come to her having to part with her Persephone. It has to happen; she doesn't have to like it either.
Hope this sheds some light, if not any help
and GOOD LUCK!
M.
PS: the longer you stay, the more grief you will have to bear for a longer time.