I really have to agree with the previous comment that this all seems to have more to do with your own self-esteem than it does the other two guys. They're just giving you something specific to fixate on, externalizing your feelings about yourself.
My husband also has moments of low self-esteem, where he wonders what a beautiful, educated woman like myself is doing with a goofy looking high school drop-out railroader like him. Sure he's funny, kind, considerate, generous... but none of those are why I love him. I love him because of who he just is. I would love him if he were paralyzed or in a coma and unable to do any of the things we love doing together. When I tell him that, he almost gets upset, telling me that he wouldn't want me to waste myself on being with someone in that state. And nothing he says ever gets me more angry than that.
I've never found lists of positive attributes to be any good for finding people to love. Never mind "people are more than the sum of their parts"... I think people, who they truly are themselves as individuals, are even completely separate from their parts. You can change all the parts of yourself: become educated, get in shape, practice conversation, learn to be funny... those are all just skills that you can learn. But none of them change who you are. I go to school with people whom I find handsome, intelligent, funny... all the things that are great in a partner. And you know what? I have no romantic feelings for them whatsoever.
Take the positive aspects you see in her husband and boyfriend, things you envy, and learn how you might incorporate them into yourself. But do it for yourself, not because you want to be more like them. Want to be better educated? Take a course at the local college. Want to be more articulate? Practice conversations with women at coffee shops.
He's tall, you're short. I prefer shorter guys, so I don't have to stretch to kiss them. Maybe she gets tired of him always talking her ear off, and really loves the way she can actually get a word in edgewise with you. And I think office guys are totally boring, whereas I love the natural muscles that labourers get just working, and greasy sweaty stinky guys working hard are SO hot! Don't assume that your differences from him are negatives!
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker