I'm replying to your comment here, instead of the Choke page because it is not really relevant to the episode and comment after comment of things that aren't related to that page could easily piss off a user and then pointless amount of drama would occur. I've been on this wiki for almost a year now, so trust me ;)
No, I don't think it was cheating, because it technically wasn't, but it is, nevertheless, wrong. It's not an act of being unfaithful to accept suggestive comments from a stranger, and it's not an act of being unfaithful to flirt back. If THAT was cheating, then what on earth would we call the whole Emma-Will tension while he was still married to Terri then?
The reason why Blaine was so hurt was not really because of the texting that was going on between Kurt and Chandler, it was because Blaine thought that Kurt wasn't committed to him anymore, and that is what hurts the most. Blaine was angry because he thought Kurt was cheating, but he was hurting because he didn't know whether Kurt was still committed to him. When you think, or you know that someone isn't committed to you or to your relationship, then, in the end, it doesn't really matter if they are faithful or not, you know that the love isn't there.