he's probably wondering 'is this all they taught her

But…can we talk about how lonely and out of place Lukas probably was before Philip?
With a father who declared is not good at feelings and who probably taught him not to show his own, “real men” don’t show their feelings and never cry”, right?
We know he has a girlfriend, except he doesn’t seem to care for her at all, even before he kisses Philip, it’s more like he tolerates her because she’s cool and thus it’s the right thing. (and since he’s gay but he obviously never thought of it, but he seems not to have any sexual attraction to her, or at least not to care, how many times must he have wondered that something must be wrong with him? ). And then there are “friends”, basically the ones he sees at school, basically the cool guys, Rose’s friends. They’re not that, not by far, so much that he’s cool because he doesn’t talk, except he doesn’t because he has nothing to say to them, because they’ve nothing in common! 
Lukas is a teen who spends his time on a bike because it’s the only thing he has. Before Philip he had no one to even talk to, to open up to. No wonder that when he saw him at school, so deeply different, he secretly followed him like a puppy waiting to talk to him and ask for photos. Philip is the only one, ever, that Lukas felt he had a chance to talk with and to, like a normal human being. Up to a point is not even about love, is about human interaction, about a deep and primal need, about something he doesn’t even fully understand nor he knows how it works.
I blame him for a few things, but how painful must have been for him to realize that only thing, that only person, was going to get taken from him forever?
Basically… Lukas is my baby, don’t touch him, he needs tons of cuddles and love!