And this is actually a reply to Debbie-san's essay about why The Lust 3 is not entitled 'The Despair'. It's certainly not a polished essay response, but it is nonetheless a response.
First, yes; lust has been defined by the Church as an adoration of the body, and it is possible to see Orihime as seeing Ichigo as an idol, as a god come to save her, a god to pray to with all of those Kurosaki-kuns whispered and spoken and yelled.
However, what is lust? Lust is an overwhelming feeling, oft described as intoxication. (Intoxication, I might add, usually refers to 'downers' like alcohol.) Lust includes the feeling of not being in control - this helplessness is often seen as a rush, as a high point, as falling madly in love or becoming delirious with love.
What do we know about Orihime?
+ Her older brother raised her and defended her, taking responsibility for her. She wears her hairpins because of this.
+ Tatsuki defended her and took responsibility for her. Orihime wears her hair long because of this.
+ Her older brother became a Hollow, and comes after her. Orihime is powerless in this situation (also traumatized by this) and who saves her? The shinigami-substitute, Kurosaki Ichigo.
It is only later that Orihime gets access to the Shun Shun Rikka, who live in her hairpins (again, symbolism there - why does she wear those hairpins?), and due to Ichigo's spiritual power, though how the influence worked (whether he caused it or simply made an existing power known) is yet unknown at this point.
In short, Orihime has had protectors, and other people have taken responsibility for her. There is a feeling of helplessness, of 'I'm not strong enough to be able to fight' or 'I'm not strong enough to participate fully in the battle'. She willingly sacrifices herself to go to Hueco Mundo. We see flashes of her defending herself (the famous Ulquiorra bitchslap), but that's all. She wants a protector, she feels helpless and weak without one.
In short, she is behaving like someone traumatized, someone who has not learned if their inner power - who does see themselves as peripheral to the main story, even though they wish to be 'whisked up and taken away' (the image of the prince's arrival, like in fairytales).
She also seems to only see herself in terms of her relationship to others; that is to say, without someone defending her she feels incomplete. (But she may always feel incomplete, due to her own insecurities - I'm just saying this might be her view on the matter.) That she needs someone to be there for her.
And so, 'lust' in this context is redefined in the feeling of helplessness - of being caught up in matters beyond one's control.