At one time, he could have actually loved Vigilance Shepard. His crush never really gained momentum as he was shot down in its early stages; Kaidan was enough of a gentleman to realize he would never beat the beautiful asari with awkward mannerisms and big blue eyes. It was a blow to the pride and his ego certainly smarted for a week or two as he sent longing glances at the commander that remained unseen. But he soon got over and the professionalism remained untampered between the two soldiers. They were still friends; maybe not the best (they certainly would never braid each other's hair or sip tea together) but when it came to strategizing or drooling over equipment, they could count on the other.
After nearly three years, Kaidan had just about forgotten his previous feelings. The events of Virmire had strained things towards the end but after her near death, Kaidan let go of any ill feelings. Shepard's involvement with Cerberus following her resurrection had cooled even the friendship they had tentatively re-established following her rejection of him. He was suspicious of her actions when she was released from prison and it nearly ruined what was left of their partnership. Honestly, a part of him would always wonder if Vigilance was still the famous commander everyone remembered her as. After all, she had a new haircut, litany of scars, and personality. The warmth in her eyes had hardened over. It was like she switched personalities with that Cerberus woman, that Lawson chick. Kaidan could almost understand. He had not realized his burgeoning feelings for Ashley until it was too late and he could never quite forgive himself for her death.
Vigilance had it almost worse. Ashley died before she knew Kaidan's feelings but, as he learned later, the Gunnery Chief had developed feelings for him. A relationship was inevitable if destiny did not snatch his chance away. But for Shepard, her love had abandoned her. Liara supposedly still harbored feelings for the hero but refused to give in as "too much time had passed." To Kaidan, this sounded like a piss-poor excuse. If you loved someone, you should hold onto them lest you regret it. He knew Shepard was taking it hard, could see it in her amber eyes and the crinkles of her smile, as fake as Saren's alibi way back when.
But, when Shepard's head was between his thighs and her mouth was unzipping his trousers, Kaidan had no room for guilt or sympathy. They both knew what they were getting into, knew that there was no going back for a re-do. This was not love, not even a pale imitation. Kaidan still felt Ash in his heart, and Shepard…well, her heart was just barely scabbed over after Liara's callous dismissal. Kaidan had. At first, felt the tang of bitterness on his tongue. Eventually Liara would leave this new persona of hers behind, go back to the meek little archeologist she was before and fall back into her commander's arms. And the major…he would be left with nothing. But now he was not so sure. Vigilance was never the type of woman to cheat, even though Kaidan guessed what they were doing no longer counted as cheating when his soulmate was blown to bits and Liara was the reigning ice queen. He had never particularly liked her anyway.
In a way, Kaidan almost felt proud. The sentinel had lost out on Shepard's heart all those years ago only to now have said commanding officer about to take him in her mouth. Not exactly what he had pictured back then but who was he to complain? Alenko had not exactly been celibate after the Normandy was lost the first time. There had been a few women, all beautiful and bland and faceless. They were nice and eased his pain for a night only to be released when the morning came. Their feelings were never hurt; they were just using him for a physical release too. The handsome, charming soldier who had saved the galaxy from Saren alongside Commander Shepard. He could have practically any woman he wanted, only they weren't even close. He was not desperately in need of human contact but if Vigilance was giving him a shot to live out an old dream of his, however fleeting, he would not hold her back.
He could fall in love with Commander Vigilance Shepard.
But, he wouldn't.