Deception Among Shakespeare's Lovers

Why do many of the lovers in Shakespeare comedies rely on deception in their romantic maneuvers? Did Shakespeare believe that this was commonplace in the realm of love? Or, did he write these scenarios purely for the sake of good comedy and in order to weave his many subplots? I'd vote for the latter...at least I'd hope for it.

In A Midsummer Night's Dream, Demetrius and Lysander both are influenced by the potion from the flower that Oberon orders Tuck to put in their eyes as they slept, causing them to fall in love with the first woman they saw. As it turns out, the both fall asleep in love with Hermia and wake up in love with Helena, as she is their first vision. Hermia and Helena both are confused; Helena believes that she is being made fun of, and Hermia believes that she's been duped by Helena. It seems like deception, but actually is not; which might add to the humor of that play. However, when Oberon has the same juice put in the eye of Titania, his own lover, thus causing her to wake and find herself in love with an ass, which indeed was deceptive. He gained some gratification of having humiliated her in that manner.

In The Merchant of Venice, the major deception among lovers is between Portia and Bassanio. Portia dressed up as a doctor of law (and thus a man) in order to save Bassanio's friend Antonio from his fate of owing Shylock a pound of flesh. Though her trick worked, she tricks Bassanio (who does not recognize her in her disguise) into giving up the ring (to the young lawyer as she was disguised) that she had sworn him to never surrender. When he returns home the next day, after her, she accuses him of having given the ring away to a woman. She toys with him in this manner until she deems it is time to tell him the truth about her game.