I'm gonna be honest with you OP if she left "all of a sudden" there was an other man and she wanted him more, far more than you, and didn't wanted you anymore. She wasn't even respectful to leave that way.
But you can be sure she has planned it a while ago before leaving, they never left all of a sudden, there always small details to notice.
If she was this way, it's not a bad thing that she left you, imagine that type of women in your life, it would be hell, especially if you signed the papers and got kids involved.
That's why you never put all in the efforts into the relationship. SHE SHOULD put in the efforts too at equal. Never stress yourself with money in order to satisfy/marry a woman.
Build your life, add stability in your life, get your money protected, get your own house/lands before signing any papers with a woman.
My fiancée could leaves me rn for whatever reason it shouldn't impacts my stability, my money, my hobbies, my passions and for what i wake-up every morning for. Protect yourself before taking care of a woman
Also, get yourself a girl who works with some stability and knows what budgeting is. Women who truly love a man don't apply any financial burden to them.