I feel like there needs to be an easier way to fill the bar during the sex scenes, I tap the button as fast as I possibly can and it still takes like 2 minutes to fill. I don't know if this is just for the Android version that is like this, however it's just made me do frustrated trying to fill the bar that by the time I did the sex scene where there were at least two bars I quit while trying to do the second bar. I would like to try again in the future, just this needs to be fixed first.
First, a quick suggestion: if you haven't already, try switching to 'easy mode' in the gameplay settings.
Regarding the issue itself, it occurs exclusively on Android devices, usually those with low and medium-level power chipsets. Unfortunately, there's nothing I can do about it, just need to wait for a newer version that includes better optimization for mobile phones (I only recently discovered how to improve performance), or try to play on one of the most powerful devices from 2022-2024. The bar fills up quickly and comfortably when the game has 50-60 FPS on the high-end mobile devices, but when the frame rate drops below this range, issues arise and the bar resists more. In easy mode, this should be much less of a problem anyway.
Another suggestion, there is no guarantee that it will work, but you can still try the following. If your phone's system settings support different screen resolutions, and you are using the high resolution setting in Android, set the lowest resolution as possible in your phone system settings and run the game one more time. Probably, this will speed up the game FPS and solve the issue.