One, I never thought of this as a fantasy site and I still don't. Two, I agree with Flaming Redhead that, just as going on a few dates doesn't make you married, exchanging a few PMs doesn't make you someone's master.

I think you are discovering that, while many interactions here might satisfy some of your fantasies, there are real people at the other end of them and they can engage your feelings beyond what your fantasies might dictate. And thank God for that. I think it says really nice things about you that you were able to connect with someone to the extent of feeling badly at her loss. I can't imagine why you thought anyone would laugh about that.

When I used to date vanilla, I used to just drop a few hints if I wasn't seeing someone exclusively. You don't have to tattoo, I'M SEEING OTHER PEOPLE on your forehead, but just saying, oh I'd love to join you but I already have plans, or something similar, can give someone that information. Similarly, if you are in communication with a few people online, saying something like, oh, hey, I'd love to chat but I'm talking with someone else right now, or even posting VMs, can just let people know that there are others you are in contact with.

On the other hand, tell your fantasies that there's nothing WRONG with monogamous relationships, even online. If your actual interactions with people lead you to want to commit to one of them, then why not?