I think online associations can become intense very quickly, it's something about the direct communication, so that might be something to do with how intensely attached you have become to her. Perhaps if you had/or did meet in real life you might have found the friendship changed anyway. In other words this may be less about the two people involved rather than the method by which you've communicated, messaging can be 'instant' and make us feel connected - if you've been missing connection in your life then you could be extra susceptible to that.

I'm not saying it wasn't a genuine friendship, but rather that the intensity may have been magnified.

It is your choice whether you ask her to 'hang out' every week or two but I'd give some thought as to whether that would really be in either of your interests. You felt 'special' because of her attention for a while but now she has a boyfriend you don't - ask yourself would chatting online every week or so be enough?

I'm inclined to suggest you start working on meeting new friends, getting out and about as much as you can, because you'd have a chance of meeting someone who you are truly special to and who will want to make you a priority without being asked. I would see this situation with your friend as an opportunity to learn what you are needing in your life.