Hmm... This is a hard one. I didn't plan on making it optional but only because I hadn't even considered it. I can see that your question has a bit of support.
I actually had a three-way relationship route in mind, where the MC and 2 girls are all kind of into eachother. (romantically and sexually). The routes will start out separate, and then there will be a turning point where the routes come together and the two girls agree they like eachother as well. Initially the idea was your previous choices would effect wether or not the melding of relationships is successful. Now after your question I'm considering keeping it like that but even once you've fulfilled all of the prerequisites, you will get an ultimate, explicit choice about if you want the relationship to actually go through.
In-game, you can atcually view each girls' sexual orientation in their profiles, some of them are hetero. There's also going to be some group sex and that can usually lead to some interaction between the girls.
Apart from the above mentioned route I don't plan on having any other girls actually be romantically interested in eachother.
