You mean the party where Anya and her boyfriend break up?did this, went to the party as well.
I wonder why that would affect things...
If you do that, you gotta go to another party until you see Anya with Roma and she says they're back together. Then the conversation option about her boyfriend can be found again, and you just talk to her about it until she asks you not to come to your room after 18:00.
Then you get a little horny and go spy on them after 18:00 a few times. Then you can interact with Anya when she's sleeping.
You can spy multiple times in one day if you have the willpower for it.