Does playing with the penis during the daytime in Ramadan, to the point of almost ejaculating but stopping it, invalidate the fast?

You erred by intentionally engaging in provocative speech and playing with your private parts during the day in Ramadan (definition). You must offer sincere repentance and not repeat the act. Your fast is not invalidated as long as semen was not emitted, according to many scholars. Some, like the Hanbalis, are of the view that the fast is invalidated by the mere movement of semen. It would be better if you made up this day as a precaution, although the fatwa (definition) we adopt is that the fast is not invalidated as long as semen was not emitted.