@Slim_dude
If your ok with some suggestions, I have a couple you might consider since it's still in beginning stages of story.
1. Alter how the love magic is received and given.
Received = any form of love related action such as a hug, a kiss (small peck, to deep probing tongues) to small sexual acts. These will produce very small amounts and must be done in abundance to accumulate enough power to sustain them both.
The real power is only obtained through vaginal sex (specifically through the female's orgasms) and can only be absorbed through the MC's penis.
Given = The manor in which it's received, it has to be giving in the same manor. Since the true power is absorbed through the penis, it must be given from the penis as well.
So the fairy has the ability (only for a very small amount of time, in the beginning) to make herself human size. At this point the MC has to fuck her to give her, her portion of love magic.
Later as he gets better at love making, he'll start to please her by causing her own orgasms.....and because of their connection anyway, she starts loving the MC as well and it will also create her own source of love magic to help them both, later in the story.
2. As it's only just one or two scenes so far, how about losing the Long Dong King Kong fleshlight dildo with suction cup for the sis. That thing is bigger than the MC, and by the time he gets to fuck her, neither one of them will get to fully enjoy it, as she will be accustomed to bigger.
I'm just suggesting that it is replaced with something smaller, maybe something that is only twice her finger size and straight.
Right now, if she soaks that thing she has in hot water, the only difference with a real one is....the real one can knock her up, and what she has, can keep her satisfied enough to be alone forever.
3. Since it seems that you're moving away from mind magic (actually that's pretty cool). How about instead, having the fairy.....since she's not seen by anyone......start doing her part by subliminal suggestions, and it doesn't have to be just the girls either.....she could start influencing the dudes too. keeping them away and possibly helping with MC's revenge on shitstain, by driving him insane or something.
Just a couple of thoughts, but I love the game and work you've done so far Brother...………………..Peace!!