My humble thoughts about that matter, which can be wrong, but I don´t think so:
Of course Nina was not jealous, because she had clearly dumped Ian at least four weeks ago. Poor guy, he is apparently still so in love with Nina, because he is sort of trying to provoke her with kissing another girl, when he does not care the least about her. There are other indicators of them being split up – him asking about the right antidepressants on Twitter, then promptly deleting the question. Him again, giving a LIKE to the Facebook group called You taught me how to love, but not how to unlove. Them both not spending together their vacations and even travels back to Atlanta, even if they used to be together 24/7 (it was almost comical sometimes). There is a rumour that he proposed to her in February because he wanted to settle and have kids (which is normal at his age), but she rejected him JUST because of that. I understand her, she is far too yound. 10 years his junior, I guess. That much have been a major blow to their relationship. But they are apparently on good terms now and support one another anywhere, which is a good sign. But they won´t say anything public about it, of course. they are intensely private, as they used to be in the beginnings of their relationship, when Ian was supposedly still dating Megan Auld (a rumour). If they told the public that they are not an item anymore, their show (they both star in) would possibly suffer from it, some die hard fans would freak out (the supporting party ofthe COUPLE) and others would possibly start chasing Ian like rockets (HIS supporters), whichwould make him freak out, I guess. So they are quiet. But I bet that if you tried to ask around, the people around TVD would confirm you that these two are already a history. My two cents about the whole matter. And sorry for my bad English. I just find it amusing that there is nobody else who could see the truth.