Question:

In my opinion, it takes a miracle to stop fantasies and sexually immoral behavior.

The Torah tells us Yosef HaTzaddik saw an image of his father and this stopped him from having sex with Zilka the wife of Potifar. If Yosef HaTzaddik was a Tzaddik, why did he need miracles to prevent him from committing a sin?

The Torah also tells us about the Yehuda and Tamar affair. Yehuda had sex with his daughter-in-law because he thought she was a prostitute.

We can see from these two cases that no amount of Torah learning or Tehillim can stop sexual urges. Since these individuals were among the most righteous people on earth, and yet they where unable to control their sexual urges, there must be another key to prevent people from engaging in sinful activity.

Tell us please what we can do to rid ourselves from sexual urges.

Answer:

First, sexual urges are healthy when expressed with ones wife at the proper times and in the proper manner. The sexual drive is the glue that helps marriage stick. We want to channel these urges, not rid ourselves of them.

Joseph Fleeing Potifar's Wife by Hendrik van Balen the Elder

1.  The Zohar teaches that Yosef was considered a Tzaddik, precisely because he overcame the seductions of Potifar's wife. Our Sages have promised that when a person comes to sanctify himself, he is given Divine assistance. This is what happened with Yosef. If you are truly serious in the battle against the evil inclination, then G-d will help you as well. Yehuda, on the other hand, did not try to sanctify himself in his roadside meeting with Tamar. He himself chose to transgress.
   
   
2. You make it sound like the miracle took all the challenge out of the test. I know a lot of people who even were they to see an image of their father or of a great sage, they would not have the internal fortitude to flee. Yosef was aided from Above by the miracle as per point 1, but still he had to choose between immediate gratification and what was right.
   
   
3. The fact is that great numbers of people have successfully overcome unhealthy lusts through a dedicated commitment to Torah and a holy lifestyle. Give it an honest try. When a person experiences the spiritual bliss that accompanies triumphing over his sexual urge, his soul pines for more and he gains added strength in his battle.

Good luck, and even though a Tzaddik will fall seven times כִּי שֶׁבַע, יִפּוֹל צַדִּיק וָקָם (Proverbs 24:16), he rises, brushes the dust off his pants, and continues his battle. It can take years upon years to overcome. The key is never to stop yearning to rise.