thread is TL;DR but...I did read the OP...here is what I think:

she wants out dude...something that stupid and simple that could be talked through and she rolls that easily...she done...it was just something she could use to justify what she is feeling...likely, somebody is in her head feeding her shite and it has made her doubt what her future is all about, but she knows it ain't with you...it hurts...but it will be a blessing down the road...

my story:
had a great chick I was engaged to...virgin, hot, blonde, caring, smart, etc....wife material...she started getting cold feet when we actually started planning the wedding and I could tell...well...my dumbass goes to a party with some friends back home...we were almost all military and on leave...she couldn't go...well long story short I kiss this chick I dated in HS goodbye at the end of the night...that was it...no sex...nothing...I was drunk and slipped her some tongue...next morning...I didn't hide it...I called her and told her and asked forgiveness...she told me it was over on the phone that day...on the phone. I never even saw her again...we had been dating for over a year and she was with me all through boot camp.....came to see me graduate and everything...we were due to get married and move to my first duty station in like 3 months...I have not seen her since 2001...that conversation was our last...we went from in love and getting married...to complete strangers in a day...and it was the best thing that ever happened to either of us...we weren't ready...I def wasn't, and she wasn't fulfilling her dreams...we would have divorced in no time...things work out the way they are supposed to..I am married now to my wife ( I met her a year later) and we have been together over a decade and have three beautiful kids...

TL;DR version: you fricked up but its a blessing in disguise