I like how she gets to decide what "resources" you "should" share----she evidently didn't have any moral issue with using your money without repayment, did she?
I appreciate that this is your friend and you don't want to offend her. I also like that you don't want to make it your roommates' fault---that's kind of you, but it *would* be ok to say "Jan and Mike and I talked it over, and we really don't want to have any more roommates. It just doesn't work for us, we're happy as we are." Then as long as you don't let someone else stay there, you're ok

"but whhhhhhy can't I just crash there? I won't be underfoot! I need the roooooom!"
"I know, and I'll help you look for a place
[if you are willing to do that, or even to just tell her what paper's website to look at, or something], but having another roommate just doesn't work for me this year."
(Notice how you can keep saying "another roommate" and not "we don't want YOU."
"But, I need it!"
"It doesn't work for me"
"But whhhhhhy"
"It doesn't work for me"
etc etc etc