No you don't need to? You can just not ask fiona for help in the competition and then that will not happen, since you can easily get three votes without asking for Grace or Fiona help.. Scott and the other weird guy its a stat test and then there's that masochist girl. Even if you ask for Fiona help you just need to not select the red haired girl and nothing will happen.You can't avoid sharing, it's just that all the forced sharing is lesbian which the dev (and a lot of people) don't seem to consider actual sharing.
For example, if you're on the sub Fiona path, you're forced to give her away to one of the judges for the art competition for the whole night.
There's no forced sharing as I know, not even lesbian, sharing Fiona is only possible because you asked for her help and you selected the red haired girl. The forced sharing are from the options you selected. For example you can force Evelyn while in her corrupted route to have a threesome with Miroslav and you. But you can also not force her if you want ( i think its only possible to force her with Miroslav by using drugs)
Selecting a corrupt path has more chances of options leading to sharing but its all avoidable.