Your self-esteem is far too caught up with this other person. Why have you handed this other person (who has proven themselves to not want the role of being the safe-keeper of your ego,) the power to grant you self-belief and value?
It's madness.
Seriously, this was a short relationship, which didn't become permanent. It wasn't some kind of competition, between you and this other woman -
as to who was the most valuable human being/most desirable woman/most perfect living soul - decided by some Olympian god.
The judgment made was not an edict to be handed down to posterity and all subsequent humans as to how to be the most perfect woman ever.
No. It was just some very ordinary guy, deciding to have a relationship with someone else.
Who knows why? Perhaps it is because she lives closer to him than you. Maybe he bases his decisions about intimate relationships based on how easy they are. Some people do. Some people (other people) would suggest this might not be the best way to choose intimate partners - but it seems to work for some people.
Perhaps she had eyes that reminded him of someone he's profoundly connected to. Maybe he doesn't even realise that. Who knows?
There's a statistic that suggests people tend to settle down with (roughly) the 12th person they've been involved with. 'Choice' in love appears to be as random (partner-wise) and determined (psychology-wise) as that.
It's honestly not worth obsessing about.
So, instead of selecting one random person out there, and trying to telepathically guess what their 'ideal' is, and then trying to (ineffectually) model yourself on that, opt for a little self-love. Work on truly accepting yourself as you are, loving yourself as you are - and then get out there again: looking for someone who loves you as you are.
Seeing relationships as some sort of 'test' whereby you have to 'come up to scratch' and be prepared to change to meet the desires of someone you set up as a judge of what is good or bad in a person (namely you) is a surefire way to ensure you have a lot of bad relationships.