Adding towards the girl-girl discussion, I'm not sure making it optional would please everyone. Not saying it in the way that you should please someone just because they'd be bothered by something being avoidable, just saying that adding content and making it optional doesn't erase the fact that a certain audience will still avoid the game or drop it once it's implemented.
I don't know about 'outrage', but you aren't definitely far-fetched in the idea that it wouldn't please a lot of people who have been playing the game thus far.
It's one thing if you had already planned to do so, but you did say that you'll make the game the way you want to, and so far you've been comfortable without adding girl x girl action, and nothing has been hinting or pointing towards said content being implemented at any point, nor in the tags or storywise.
Also, it's usually detrimental for people that don't enjoy that type of content, since it sometimes becomes the main focus of some scenes and usually doesn't have an alternative, meaning that you just end up missing out on content.
Example: a threesome in which you have a chance for the women to play with each other, the pattern usually goes 1) you let them do it and get the full scene or 2) you don't let it happen, and you either miss a bunch of renders, or the whole scene altogether.
Therefore, it's also extra work and effort from your part it you want to please both crowds in adding an alternative scene or set of renders just so that you don't feel you're lacking. Even so, you would of course never please everyone 100%, that's impossible in any game

Or, you can simply let things unfold as they have so far, and keep the people that don't enjoy that content happy, while keeping the ones who do enjoy it 'mildly' content, even if they'd like for that to happen.
Either way, this is your game after all and of course you'll do what you deem best. I'm usually on the fence with that type of content, although I usually avoid it since it isn't really my cup of tea and I tend to find myself uncomfortable in certain scenarios like that, so indeed my opinion might be a bit biased.