Do bad dreams come true, even though they are from Satan and I have not told anyone about them?

You did well by not speaking about your bad dreams. You must, however, persist in reciting the recommended supplications and protective prayers, such as:

The supplication: "O Allah, I ask You for well-being in this world and the Hereafter. O Allah, I ask You for forgiveness and well-being in my religion, my worldly affairs, my family, and my wealth. O Allah, conceal my flaws, O Allah, protect me from before me and from behind me, from my right and from my left, and from above me, and I seek refuge in Your Greatness from being unexpectedly struck from beneath me." "O Ever-Living, O Self-Sustaining, by Your mercy I seek assistance. Correct for me all my affairs and do not entrust me to myself for the blink of an eye." "Allah is sufficient for me; there is no god but Him. In Him I put my trust, and He is the Lord of the Magnificent Throne" seven times. "There is no god but You; glory be to You. Indeed, I was among the wrongdoers." "O Allah, I ask You, for Yours is all praise. There is no god but You, the Giver of all good, the Originator of the heavens and the earth. O Possessor of Majesty and Honor, O Ever-Living, O Self-Sustaining, I ask You."