[Decel]

I believe that he goes for Haruka after she wakes up because she appears the weakest at the time. As you say, he doesn't notice how much he's hurting Mitsuki until he finds out she's quit her job and moving and all. At that point Haruka was -or rather appeared- stronger than Mitsuki (she started therapy and all by herself).

Accident, then:
-Haruka in a coma <- Goes after Haruka
-Mitsuki breaks down crying (and getting naked) <- Goes after Mitsuki
-Haruka wakes up, thinks she's 3 years in the past (Mitsuki appears fine at that time) <- Goes after Haruka
-Mitsuki breaks down, quit jobs, moves out. Haruka gets "stronger" (ironically, to be with Taka), takes therapy <- Goes after Mitsuki

As I've stated, Taka's a reactionary character that goes where he's needed most. There was a whole debate over it in another thread.