In the story of Bleach, there is room for a little romance between battles and comic relief during each story arc, and much of that romance centers around Inoue Orihime, one of Ichigo and Uryu's classmates and a fellow citizen of Karakura Town. Ultimately, Orihime married Ichigo, as the Bleach manga's final chapter showed, but Ichigo had a little competition until then.
Ishida Uryu is another of Ichigo's classmates and secretly a member of the Quincy tribe. Uryu declared himself Ichigo's rival as a fellow spiritual warrior, but subtly, both boys were also romantic rivals, and Orihime's affection was on the line. However, fans might wonder what drew Uryu to Orihime in the first place, and there are a few plausible explanations for this.
Uryu Has A Chivalrous Nature, Especially Where Inoue Orihime Is Concerned
Uryu is like a foil to the hotheaded and impulsive Kurosaki Ichigo, and not just for the sake of creating amusing chemistry between these two characters in the story. Uryu is an honor-bound and chivalrous person who takes the honor of the Quincy tribe seriously, and even Captain Kurotsuchi Mayuri has commented on this. He noted how the Quincy regulate their actions and speech with their code of honor, and Uryu feels the same way. He acts not just on his own behalf but as a representative of the Quincy tribe, and that includes his treatment of others. Uryu pressures himself to be the perfect gentleman.
Uryu acts politely and with dignity at all times, and he is a good student on top of that. Most of all, as a proper Quincy gentleman, he treats girls and women with the utmost respect and takes it upon himself to protect them and their happiness. It's true that Orihime can use her own supernatural powers to protect herself, but all the same, Uryu's honorable Quincy code demands that he look after her and put her needs first.
This is reflected in his actions during the "Soul Society" arc, when Uryu risked his life to fight Captain Kurotsuchi and shield Orihime from his wrath. Later, Uryu risked his life once again to rescue her from the depths of Las Noches in the "Hueco Mundo" story arc. Along the way, Uryu's protective and chivalrous feelings gave way to something more personal, and he protected Orihime as more than a Quincy gentleman. For him, honor and personal interests had finally intersected in the best of ways.
Uryu Found Warmth In Orihime He Didn't Find With His Own Family
There's another probable reason for why Uryu developed a seemingly inexplicable crush on Orihime: her warm personality. At first, Uryu and Orihime seem like total opposites in terms of personality and worldview, but that actually makes them compatible. Uryu did have a warm relationship with his grandfather Soken, who trained him, but Soken was killed by the Soul Reapers, and Uryu grew bitter and hateful as a result. Now his memory of Soken is soured and he can't even find comfort with his parents -- certainly not his stern and aloof father Ryuken. Uryu can't find any warmth or joy in his family, so naturally, he craved it from another source.
Uryu found in Orihime what he couldn't find in his own family, and that helped motivate him as a fighter and soothe his wounded heart. Orihime had an even more positive effect on Uryu than she did on Ichigo or Chad, and Uryu quickly became a better person for it. It's only natural that Uryu would develop a crush on Orihime, his heart's way of acknowledging what he has done for him and thanking her for it. Thus, Uryu grew highly protective of his friend and sole source of personal warmth, and his protective feelings easily rivaled Ichigo's.
It's not clear whether Uryu ever felt jealous of Orihime and Ichigo's eventual marriage later in life, but it's conceivable that the older Uryu sometimes wonders what if? Uryu is definitely enough of a romantic to think about it at least once or twice in his life.