Actually, it is as simple as he makes it out to be. You're complicating it with excuses because you don't want to deal with the financial consequences of leaving your boyfriend. You may have some false sense of respect for yourself, but it's obvious that you don't actually respect your boyfriend and he deserves better than that.
No, you're screwing around with someone on the internet that isn't actually real. You can start a relationship online, but you can't actually have a real relationship online. It just doesn't work that way. What you get is a pseudo person putting on a show for you to make you believe you're something that you're not.
As for sex. Sure guys like sex, even better they like easy sex. But frankly most guys are a lot more complicated than wanting to just get laid.
Sounds like you're just full of excuses as to why you shouldn't do the right thing both for yourself and your boyfriend, and because of this you have no problem being involved with someone else who isn't actually available either.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."