Selina Kyle/Catwoman
Bruce was going to marry her. What more needs to be said?
They understood each other, they accepted each other and more than anything else, gave each other the strength and confidence to grow into their best selves. For 80 years, they flirted, fought, dated and survived crisises, Zero Hours, reboots and retcons. Regardless of who they were with, which parallel universe they were on, or how badly Barry Allen messed up the timeline, the Bat and the Cat always found one another. But Bruce lost her to Batman all the same.
This, apparently, condemns Bruce to crime alley. Selina Kyle was his best chance, the strongest tether he could use to climb out of the abyss inside himself but Catwoman decided that Batman was too important. And despite how much it pained and devastated the both of them, Batman had to live or, frankly, their world would die. So she left.
Bruce Wayne is, of course, broken. Selina just proved that everything he feared about wearing the cowl is true, that he cannot be the Caped Crusader and be happy. However, this tragedy doesn’t make him a hero, he’s a hero because he chooses to be Batman despite this tragedy. He chooses to be Batman knowing that he will sink deeper into the abyss, understanding that he will never know a better tomorrow, and welcoming the promise of more horrors. Bruce Wayne is a hero because he realized that he’ll always be broken but vowed that his world will be better for it.