what role does Malvolio in Twelfth Night, especially in the viola-olivia-orsino love triangle? does his fate seem unjust? is it out of place in a romantic comedy? If so, why might Shakespeare have included it?

In my opinion, Malvolio's character adds a twist that incites both humor and pity. He's the straight man who goes wrong, throwing away his piousness in the name of greed. His fate might seem unjust, but his character also seems to be a bit of a cautionary tale, which Shakespeare very carefully throws into the comedy for good measure. Shakespeare's inclusion of Malvolio definitely cautions against dreams born of delusion..... fooling ourselves into believing the impossible. One can dream.... but one also has to keep an eye on reality. Malvolio lost his reality, something that in the end, leaves him with a desire for revenge.