If you had an "internet friend" that you never met in real life, and they suddenly stopped sending you emails and IM's, would you ask them why?

I “met” this guy on a website (not a singles or dating website) and we started corresponding and became email friends. We had several nights of IM’ing and we were planning to meet. All of a sudden, when he was typing out a joke (you know how it says the person “is typing”) he stopped and said he had to go, very quickly, totally out of the blue. He was still showing as “available,” in other words, he was still on Yahoo after that. To me, it was apparent that someone else started messaging him. I had to admit I was kind of insulted (whether or not that’s justified, I don’t know).

That was about a week ago, and I often see him on Yahoo as “available” but he no longer tries to contact me. Should i ask him what happened, why he no longer gets in touch? or should I just let it go?