Title text: If you've never had sex, this is what it feels like. Complete with the brief feeling of satisfaction, followed by ennui, followed by getting bored and trying to make it happen again
This comic is a reference to the video game Tetris, in which you use different shaped pieces to fill in lines to score points. The more lines you fill at a time results in more points.
In this comic, Heaven is when you get the perfect piece in Tetris that fills out all the empty space you have on the board.
In the image text, ennui means a feeling of utter weariness and discontent resulting from satiety or lack of interest.