There is a big Exile button at the bottom of the screen , portal will become available inside it once you reach a particular part of story (just 2 events needs to be triggered manually for that after moving to Exile), it will reappear.
Until then click through all other options inside that button
Complete the other signals/ girls hints, girls in portal disappears sometimes and wont appear if some of these dependencies are not done and may I suggest look around the house there are lots of new rooms in it, and yeah most of the events are time specific, so check through all time if you feel like stuck.,