I met a girl online who seemed to be the dream girl. Due to her busy last weeks of class & then pandemic our relationship was 90% long distance. She was sweet, kind, positive, happy & seemed very emotionally intelligent. I’ll skip the good honeymoon description but our relationship evolved to long calls, falling asleep on the phone, plans to visit me in the summer (even before meeting me), plans when I get back, virtual walks etc. She thinks im amazing, supportive and has never felt this way before, and it kinda scares her. A lot of cutesey
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"where it all went wrong" is not entirely clear. she gave you clues...i would bet some money that they are just pieces of a bigger puzzle.
a whirlwind, passionate relationship can be a beautiful, fun thing.
it can also be very misleading.
you can spend 24 hours talking to a person, each exchanging life stories, and connect on a passionate level. ive done it a number of times myself. it can be misleading in that intensity can be mistaken for intimacy. it can feel like youve met your soulmate, when in fact, really and truly, you dont really know each other yet. that same person you spent 24 hours talking to may not actually appreciate it on the same level, may even barely remember it the next day (im using an example, not saying that is what happened here).
I can't stop wondering if I found my match and I ruined it, or why her ex got a year with her while I got like 3 months. It makes me feel defective.
more than likely, you did not meet your match, and you did not ruin it.
more than likely, the two of you just werent on the same page, and didnt pan out. it happens

it hurts like crazy because you invested strongly, and i think anyone involved in something so passionate would be hurt and wanting for answers.
as i said, the answers arent entirely clear.
i suspect that her affections and plans were overstatements. not that she didnt mean them, but in the same way that ive probably told every girl ive dated that they are "the most beautiful girl in the world", or girls have told me im "the best boyfriend ever".
has had concerns for a bit
and i suspect that underneath all of that, more was going on that you werent privy to. what that was is hard to say. maybe she had doubts. maybe shes fickle. maybe others were in the picture. this is the case in virtually every breakup...we just often arent privy to it.
She tells me she doesn’t want to get in to it.
this is speculation, but its also possible that the reasons that she gave you may have been more in hindsight, than a reflection of what she was feeling at the time. kinda like (crude example) when youre dating someone, you love everything about them, all their ways and quirks, and then when you break up, all those things drive you up a wall.