He actually takes Melissa's comments to heart and realizes he is a crappy prince and decides to let her and Yuri alone as he goes on wanting to be more involved with politics rather than sleeping around, he also decides to stop hanging with bad influences, one of which is Jake as Jake just allowed him to do everything he wanted even when it was blatantly cheating on his sister and Jake blaming Melissa for it.
Yes, Ian gets character development and realizes what a bastard he was, yes, he eventually decides Jake sucks too and would probably drag him down to how he was before...Jake, believe it or not, is angry about this and blames Melissa for going too far with her plans to spite Ian and make him jealous in hopes he would come back...because he still believes she loves Ian even after all of this and outright thinks that there is no way Ian would ever come back because Yuri is superior in every way.
...Jake has absolutely no respect for Melissa and i am starting to see why Ian thought he would be a bad influence.