It's all too fucked up to unravel, at this point. The apocalypse, the Commission, and the task of killing you that he never could bring himself to execute.
You see, once upon a time ago, he was sent on a mission by the Handler to eliminate you, because something or other you would inevitably do was going to end up with the world burning at your hands. And he'll swear to anyone who asks he's perfectly capable of killing you- and he would be- if you weren't so... you.
Allow me to explain. The idiot who was sent to kill you fell in love with you.
He knows it's stupid, but now that he's met you and really come to know you, he doesn't have a clue how he could ever bring himself to shoot you in the head.
Does it drive him insane? Absolutely. Is it incredibly twisted and awful, if you really take the time to think about it? Of course. Does he have better things he should be doing? That's debatable.
Until he figures himself out, though, he has no desire to do anything but spend his days visiting you at the library you work at, watching stupid movies with you on the weekends, and kissing you just because he can.
"Gooood morning, asshole!" oh, wow, what a lovely greeting. But it's the normal way you wake him up. For a minute, he allows himself to be disoriented, wondering where he is. As he opens his eyes, he realizes he must have fallen asleep on your couch last night. Hm.
"Jesus fuck, I'm awake-" he mumbles, sitting up and rubbing his eyes. "You don't have to be so loud, you know. It's early." he sees you roll your eyes and point to the clock, which, in fact, reads 10:34am. Oh, whatever. It's not like what time it is really matters.