You don't need to be so dramatic (especially since he doesn't only get on you about this stuff, because if that was the case then I kind of wouldn't blame you, but that's not the case).
Quit if you want to, that's your choice and no one is going to stop you.
If it was me though, I'd either post in all the RPs I needed to post in if I was on or post in none of them, especially if I was worried about illegally using someone else's Internet (but in that case, I wouldn't use it at all). But that's just me and I can't (and won't) tell you how you should do things. It's just some advice.
Anyways, have fun with your other RPs. I hope you enjoy them.
(And I apologize if I sound like a *** but I don't do well with attitude...which doesn't make sense because I can have quite an attitude.)