Reasons;
Because they are partners.
Because they've both lost a significant other.
Because they both have issues.
Because he can hold his own against her.
Because they both want the black boxes and Division destroyed.
Because they have chemistry.
Because he's the first guy Nikita undresses in the first season.
Because it's so wrong that it's right.
Because he knows she's "bossy like that."
Because he takes care of her.
Because he apologized about Daniel.
Because they shared a heartfelt goodbye hug.
Bceuase he cooked tofu scramble for her.

http://24.media.tumblr.com/tumblr_lk...py5lo1_500.gif
OWEN: Nikita. I never apologized… for Daniel. I’m sorry. I’m sorry.
NIKITA: Take care of yourself, okay?

http://24.media.tumblr.com/tumblr_md...zae8o1_250.gifhttp://25.media.tumblr.com/tumblr_md...zae8o2_250.gif
http://25.media.tumblr.com/tumblr_md...zae8o3_250.gifhttp://24.media.tumblr.com/tumblr_md...zae8o4_250.gif
http://25.media.tumblr.com/tumblr_md...zae8o5_250.gifhttp://25.media.tumblr.com/tumblr_md...zae8o6_250.gif
Source

DEVON SAWA: "I think he absolutely loves Nikita.
It’s something we haven’t explored fully yet,
but he’s got a connection with Nikita.
They have similar backgrounds;
they were both screwed over by Division and Percy.
They’re very similar in a way and that’s why he’s so drawn to her."

POTM;
http://24.media.tumblr.com/30e055b9f...x6yyo1_250.gifhttp://25.media.tumblr.com/104ab0717...x6yyo2_250.gif
Source

Future Thread Titles;
"Nikita and Owen have just gone through a lot of the same things."
"We get each other. We’re hard-trained assassins with heart."
“The nice thing about Owen and Nikita is that they get each other."
"That’s the nice thing about their relationship; they’ve been through the same thing."
"They get each other; he trusts her; and he knows she trusts him."
"You always knew what was best for me, didn't you?"-Owen
"I’d forgotten how bossy you can be. And well, I kind of missed that."-Owen
"There’s more to Owen than you think."-Nikita