'Twelfth Night' consists of many love triangles and the different characters involved in the triangles don't end up with the ones they love or even their love makes them blind to see that the person they love is their same gender! An ideal example of true love is Viola's love for Orsino. She falls in love with Orsino at first sight of him; however, she has disguised herself as a man and as she is unknown in Illyria she finds it very difficult to express her love to the Duke directly; although, she always hints him that she is a woman and loves him a lot during the play.
"Viola: To woo your lady. [Aside] Yet a barful strife!
Whoe'er I woo, myself would be his wife.
Viola is a true lover because she is very sincere to Orsino throughout the play; moreover, obediently carries out Orsino's orders to woo Olivia; she tells Olivia what genuine love really is like and she is willing to die for love.
There was another true love situation; however, this time Viola was on the receiving end. Viola was given the job to woo Olivia, it went completely wrong and Olivia started to have affection for Viola instead. Olivia thinks very highly of her: 'Is't not well done?' Olivia didn't know that Viola was a woman; however, Viola knew what a woman would like to hear from a lover; therefore, Olivia fell in love with Viola. Olivia equates love with sickness.
"Olivia: Even so quickly may one catch the plague."
Viola was in a very difficult situation to tackle; either she could tell everyone that she is a woman but that would eliminate the chances to get Orsino to love Viola. Viola hopes time will solve her problem. She faces a lot of troubles and unhappiness when Olivia falls in love with her.
"Viola: O time, thou must untangle this, not I;
It is too hard a knot for me t'untie."
There is also another true love situation: love between Viola and Sebastian. Viola loves her brother a lot and thinks that she has lost him in the ship wreck which she survived and mourns for her; moreover, Sebastian thinks the same and mourns for her too. Olivia also has lost her brother but she forgets about him when she falls in love with Viola.
"Viola: O my poor brother! And so perchance he may be.
"Sebastian: ...she bore a mind that envy could not but call fair.
The second type of love in 'Twelfth Night' is false love (not true love). Orsino's love for Olivia is perfect example of 'false love'. Orsino claims that he fell in love with Olivia at first sight. Orsino is given a very unique tone or language (by Shakespeare) which clearly speaks out that his love for Olivia is false.
"Orsino: Why so I do, the noblest that I have,
O when mine eyes did see Olivia first,
That instant I was turned into a hart..."
Orsino is very moody: 'Enough; no more'. He constantly talks about love: 'O spirit of love'. He thinks that his love for Olivia is greater than anyone else's: 'my love more noble than the world'. He thinks Olivia will fall in love with him: 'one selfsame king'.
Orsino thinks that Olivia is always dreaming about him and he thinks that he is the perfect example of a true lover because he always in Olivia's thoughts.
"Orsino: For such as I am, all true lovers are,
Unstaid and skittish in all motion else,
Save in the constant image of the creature."
Orsino is not the only one who loves Olivia but can not achieve her; Sir Andrew Aguecheek and Malvolio also love her but can not obtain her. Sir Andrew is the most stupid character of the play. He is Sir Toby's friend and Sir Toby persuades him to love Olivia. Sir Andrew being very gullible and trusts his friends he tries to woo Olivia. Olivia rarely talks to him during the play and like everyone else; she also thinks that he is an idiot.
Malvolio is also a very unique character in this play. He is a puritan and defies Sir Toby's 'cakes and ales' philosophy. He is very pompous and a gullible character. He is very critical about people below him. He is sick with self love.
"Olivia: O you are sick of self-love, Malvolio."
Malvolio also has secret fantasies that Olivia loves him and he doesn't realise how stupid he looked like when he followed the letter but his self-conceit caused him to fall for the trap very easily.
The third type of love is friendship. Friendship between Antonio and Sebastian is a fine example. Antonio first saves Sebastian from the 'jaws of death', then his love ('more sharp than filed steel) follows him to his enemy's territory knowing the danger he would have to face. Antonio supplies him money which he can spend on souvenirs just like a parent would give to his child. Their friendship is very pure and clear; however, Antonio hated Sebastian for a while as he asked money from Viola and she just gave him a few coins mistaking Viola for Sebastian.
There is a friendship between Sir Toby and Sir Andrew. Although, Sir Toby uses Sir Andrew's money and make fun of him; however, Sir Andrew accepts him as a friend until the end when Sir Toby insults Sir Andrew.
"Sir Toby: Will you help - an ass-head, and a coxcomb, and a knave, a thin-faced knave, a gull?"
All these relationships affected each character one way or another. Orsino was very unhappy as he figured out that Olivia didn't love him but still he found Viola to love. Viola was happy as she achieved what she desired. Olivia also did not achieve whom she wanted; however, she loves Sebastian and found happiness after her father's and brother's deaths. Sebastian finds his sister and finds happiness with Olivia. However, Sir Andrew and Malvolio are rejected and do not find happiness like rest of them do, Sir Andrew leave unhappily and Malvolio promises a revenge.
As a conclusion, Shakespeare not only wrote a comedy to make people laugh but also explains what love really is; how love can affect ones life; how people forget their status when they are in love; how people feel when they fail to achieve what they desire. So 'Twelfth Night' is not only about making sexual jokes after all!