"Birds of a feather flock together" is more than a trite saying~ it's an inalienable truth.
You've heard me say, like attracts like. Hard as it is to accept or believe, we are drawn to others who match our own vibration. Our emotional development is mirrored by another, and this is what makes a union between two people feel like it's a fit.
When you recognize the deficits in someone you're dating, but ya wanna hang in there, you're choosing a partner who echoes for you your own deficits. Oh, it's easy to think, "I'm so strong now, I can help him/her grow and heal too" but it's never the case.
Who we choose romantically, SHOWS us where we ourselves, are lacking. Denial keeps us from recognizing our own deficits, particularly if we've fought hard since early childhood to surmount our insecurities or emotional setbacks. It's literally the element that draws SO MANY psychotherapists to partners who have Borderline Personality Disordered traits, and keeps 'em there.
If you clearly SEE the fragile or broken parts in someone you're attracted to, let yourself understand that these are the areas where your own emotional growth got stunted during early childhood. I know it doesn't SEEM that way, because you think of yourself as somewhat invincible now, and believe you can fix anything and anyone else, but a fragile partner is mirroring your own (denied) weaknesses.
Helping clients recover from a toxic relationship was the easy part of my job. Assisting them in mending from childhood trauma and growing genuine self-worth so they could become emotionally whole/healthy self-actualized individuals who finally had the ability to feel DESERVING of adoration from a partner, was a lengthier process.
Some had the exceptional courage it takes to build that essential foundation for themselves, others did not. I guess if "Happiness" weren't so elusive for many as they're growing up, it would be tenaciously sought after by more.