Video 1: link
In this video (an interview with Ryan Seacrest), Nick was asked if he is dating Selena. He didn't say if he was 或者 wasn't, but watch how he reacts to the question. While stating that Selena is "An amazing girl" and that "anyone would be lucky to be dating her", he can't help but smile. Another point I would like to bring up about this video are the reasons why he wouldn't say yes 或者 no. He can't honestly say `no, we aren't dating` becase a)they are dating, b)they would be constantly bugged 由 the press about it, and c)it could put a strain on the relationship.
If this video isn't enough proof, there is one 更多 video in which Nelena is confirmed.
Video 2: link
Right as the video is starting, Cody Linely was asked if Nick was dating Selena. He doesn't hide it 或者 say it's not his business. He clearly states that they (Nick and Selena) are dating.
There 你 have it. In two different videos, undeniable proof that there is in fact, a Nelena.
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UPDATE!:
A third 来源 has been found confirming Nelena. Here is the link to the article: link
The 文章 is from PEOPLE magazine, regarding Nelena's first kiss. It is also mentioned below in Leytonfan4ever's comment.
