It's interesting, we were actually discussing the very same topic in my Philosophy class yesterday. From what I've assumed and gathered, an online relationship that starts online can be a real relationship, but it is likely strained for several obvious reasons. Most people would contribute the lack of face to face communication as an indicator of a relationship in turmoil, but since that is essentially what online relationships are, I guess it's safe to assume that some people find it easier to deal with in certain ways. Living life behind a screen allows for people to manipulate their person online, often crafting it so that it is appealing to many others. Not to say that every relationship is like that, but that's definitely something that happens. Of course, it is very possible for reality to mix with online life, as has been witnessed on this very forum. Captain Fabio and Kura are the best examples that come to mind; they met online here, and are now in a very happy relationship, as they see each other and everything.
Personally, I've looooong since given up on it, like 4 years ago. And it wasn't even an online relationship more than it was a crush. I just realized that the commitment it'd take and the hardships I'd face were not, in my eyes, worth it. But, of course, whatever floats your boat. I'm genuinely happy to see people be happy together, regardless of medium.