I think the implication is that Kavinsky took advantage of Ronan while he was under the influence.

I have a massive soft spot for Kavinsky, even though I know he is a terrible horrible person. The implications that he might have killed his father, that he dreams people into being his servants and playthings, that he supports his mother's drug addiction. He is a sadist, a bully and a possible rapist - these are all the things that should make any one run away screaming NO - and yet. Even Maggie admits to liking him.

If you haven't had a chance to read her pretty lengthy tribute to the dichotomy that is Kavinsky/Lynch in Dream Thieves it is totally worth finding.

(Sorry for the lengthy ramble! I just really love talking about this boy! <3)