I think he fell in love with her at first sight. The way he stares at her in "Necessary Evil" when he first spots her is one of "Oh ... my ..." He definitely found her beautiful - hence the phrase he says to her regarding her beauty, which she takes as his attempt to make a pass at her. She treats him first as a regular man and then as a security officer, but not once as a being completely different - which is a treatment he's gotten all of his life. That makes him feel as though they are on equal footing, conversation-wise. He could have turned her in just for being a rebel, but he had already started to feel ... something ... toward her. She wasn't just another Bajoran to him. When Quark makes a lewd comment about Kira, Odo's reaction is instant - he hoists the Ferengi (whom he just met) off his feet ... much the way he would after they were a couple.

By the time she is transferred in Season 2, he's completely in love with her ... and the idea of remaining on the station with her gone frightens him, devastates him, and angers him. He had stayed, IMO, for her, when he could have left once the Cardassians did. He wants her to fight against it and to stay ... for him.

I think it was love at first sight, although I'll bet Odo didn't define it as such. He probably had no idea what to call it, only that she touched him in a way no humanoid ever had. The flashback in "Necessary Evil" also shows us how his feelings for Kira cause such a conflict for him - his 'justice trick' instinct warring with his new-found protective streak that is equally instinctive. I've often wondered what Odo would have done had he known Kira had killed Va'atrik - would he still have protected her from Dukat? I think he would have. Thankfully for Odo, he didn't need to make that choice.

If you look at their early interaction, I think Odo's emotional attachment to Kira is obvious. "Past Prologue" shows that Odo has already earned Kira's complete trust. "A Man Alone" Odo confides in Kira. Odo offers emotional support to Kira in "Duet" and clearly Odo is frantic by the time Kira is forced off the station.

Since the writers didn't come up with the idea that Odo loved Kira until "Necessary Evil," I think the spark that showed up between the characters before that episode is a testament to the chemistry between Rene and Nana. With any other actors in those roles, we would never have had an Odo/Kira. Thank the Prophets for the DS9 Casting Director (and for Michelle Forbes decision to pursue other interests!)

LOL I just can't see anybody but Kira on DS9 as Bajoran liason officer.

In my opinion, his love for Kira definitely guided his career choices - who knows what he would've done with his life if he hadn't met Kira on Terok Nor during the Occupation. Would he have still stayed on DS9? Perhaps, perhaps not. But it seems he had lived a miserable life at the laboratory and had run away from it, maybe only accidentally finding a life in law enforcement/security. So to find a beautiful woman who treats him as a regular person instead of a freak (and who actually treats him with respect by addressing him by rank), probably would've given him a moment's inspiration about maybe staying near said woman - though not necessarily going back to Bajor. Once Kira was stationed on DS9, he knew he was staying there too. By "Emissary" Kira's addressing Odo by name instead of "Constable" (in "Necessary Evil" I don't recall her knowing his name in the flashbacks). They're also more friendly ... and you would never know they had met under awkward suspect/policeman circumstances.

Don't know what Odo would have done as far as a career. I've always wondered about how he came to be on Terek Nor. Did Dukat send for him (it was mentioned Odo was in the mines on Bajor, and used to settle disputes between Bajorans, presumably somehow connected with the mines), or by this time was Odo settling Bajoran disputes on Terek Nor? He seems familiar with the station (he knew what was on Level 22), but I always had the impression Dukat fetched him to Terek Nor from Bajor. Any ideas?

I'm guessing once Odo became aware that Kira was going to be the liaison officer once Star Fleet took over, his decision was made. Of course that decision would also have involved the new Bajoran government. I'm thinking that Kira might have had something to do with his being commissioned into Bajoran Security.

As to the impact Kira had on Odo, he was definitely affected by her beauty, but I think it was the way she challenged his belief that he was the outsider who didn't ever need to take sides that hit him like a blow to the gut. Odo's whole sense of self-identity was defined by his being the alien freak, the outsider who felt alienated by everyone around him. Then here comes Kira, treating like an equal and a person, respecting his ability as an investigator even while disagreeing with his decision to work for Dukat. And then she completely knocks him for a loop by taking on his primary core value that as the outsider he doesn't have to take sides. She has managed to totally redefine him in a matter of a few days.The fact that Odo doesn't resent the way Kira has turned his life upside down is evidence that he has deep emotional feelings for her. And that theme of choice is a thread that runs through the remainder of Odo's life. His choice about his job, his choice about his people, and his choice in regards to Kira.