The seventh word in Twelfth Night is "love" and that sets the tone for the rest of the play. From then on almost all that is spoken about is love in some form. Whether it be in the context of pain or pleasure the play gives a slightly comical insight into love.
The play's opening speech includes one of its most famous lines, as the unhappy, lovesick Orsino tells his servants and musicians, "If music be the food of love, play on." In the speech that follows, Orsino asks for the musicians to give him so much food ,which he uses as a metaphor for love, that he will "surfeit" and cease to desire love any longer. He also uses words like "sicken" and "dying". These are both associated with pain not pleasure and this is how he has felt ever since he has seen Olivia and she has rejected him.
Through these words, Shakespeare introduces the image of love as something unwanted, something that comes upon people unexpectedly and that is not easily avoided. Orsino is in so much pain that he thinks his senses are failing; things are "not so sweet as they were before". After hearing the news that Olivia will be mourning her brothers death he is distraught and also very angry. He says,"To pay this debt of love but to a brother,how will she love, when the rich golden shafthath killed the flock of all affections else."Orsino feels that it would be very selfish of her not to love him. But I think the greater pain that he is feeling is that after seven years she will not be as beautiful as she is now, so then he may not want her, which is a very self centred way of looking at things.