She clearly has some semblance of what love is, just that she doesn't quite seem to grasp what goes into the border of romance and why. Frankly, it initially seemed a bit contrived to me as well, but looking back, her actions seemed consistent to this fact.
For a start, the reason they started kissing was because they wanted to do something to prove that their 'friendship' was special. In episode 2, some time has passed since they first kissed and Haruka's comment about Yuu 'not being like that' gives away that they haven't kissed much,if at all since then. However, the two refer to kissing as sharing a 'secret', this enforces what we saw last episode, that kissing was something to prove that they are special to each other in an otherwise 'normal friendship' .
In episode 5, Haruka nearly kisses Mitsuki as part of a play(thankfully stopped by Yuu). In episode 8, indeed she mentions marrying Yuu, that's nice and all, but she clearly only vaguely understands marriage since, well...it might not be possible. So anyway, later in the episode, she starts to feel heartache and doesn't know what this emotion is nor does she know how to deal with it. It might not be worth mentioning, but we do also see that Haruka has a protective father.
Well, in the context of our own lives, the fact that they don't understand love, this fact alone can be enough to make it feel forced. I personally believe that this sort of naivety can exist, accounting the cultural differences, their own background and the fact that they don't seem to own computers, but that is just my opinion.