Within Shakespeare's Twelfth Night there is romantic love, narcissistic love, and friendly love. Orsino, Olivia, Viola, and Sebastian participate in romantic love which ultimately leads to marriage, which is an ultimate bond. Malvolio attempts to participate in romantic love when he is duped, but he demonstrates fully the ways of narcissistic love by propping himself up above the other servants and Sir Andrew and Sir Toby. Antonio, though, is the character who exemplifies the bond of love that is created in loyal friendships, but also seems quite quizzical to modern audiences when he uses the word "love" to verbalize that loyalty. In the case of Antonio's love for Sebastian, one might wonder what type of love he has or how it drives him to be so protective of and loyal to Sebastian.
Antonio is an experienced sea captain who saves Sebastian from the storm. Being thus experienced, this would suggest that Antonio is older than the young Sebastian. It is possible that Antonio's love and loyalty might parallel that of a protective father. Antonio allows Sebastian to stay with him for about three months, and during that time, he nourished him back to health. These two most assuredly over such time they formed an intimate relationship of trust. Also, the two made it out alive together and may have bonded in the joy of survival. They get so close that Antonio grieves at the fact that Sebastian could have lost his sister to the storm (II.i.20).
Later, Antonio describes his bond to Sebastian by saying,
"I could not stay behind you: my desire,
More sharp than filed steel, did spur me forth;
And not all love to see you, though so much
As might have drawn one to a longer voyage,
But jealousy what might befall your travel,
Being skill-less in these parts; which to a stranger,
Unguided and unfriended, often prove
Rough and unhospitable: my willing love,
The rather by these arguments of fear,
Set forth in your pursuit" (III.iii.4-13).
Clearly, Antonio has played the part of watch-keeper and caregiver for Sebastian so long that he feels compelled to continue it even at the risk of his own life.