"Each one should remain in the situation which he was in when God called him" (1 Corinthians 7:20).
Years ago I had learned of a man who had struggled greatly with lust and become grossly entrenched in the bondage of pornography. Longing desperately to be separated from this long-time struggle, he mistakenly assumed that getting married would set him free. Not only did he find that he was in error in his thinking, he found that the fight would continue. There would be no "easy way out." He would have to engage with the power of God and depend upon that strength to endure. And that, he did.
Like this man who found the freedom he desired in Christ, yet found it through the process of dependance and endurance, so are many. Paul addresses an issue here in the context of many things. He's addressing marriage, slavery, ceremonial obligations and traditions. The point he makes is clear and applicable both then and now. When someone comes to Christ, there is NO GUARANTEE of immediate resolution of all struggle. The fight will continue. However, the source of your fight will change. It is no longer you, your will, or your strength. Rather, it is your surrender unto Jesus. He, then, gives you the resources you need and the resolve you will depend on in your quest to see that freedom realized.
It was for freedom that Christ has set you free. This is true. What is also true, is that everything you need for that freedom is found in Christ and is finished in Christ. But what is further true, is that you have to daily walk it out and work it out in fear and trembling. You have to take captive every thought and imagination that would attempt to exalt itself over the knowledge of Jesus Christ. You have to depend upon Him and lock-eyes with Him as the author and perfecter of your faith. Don't be afraid of the struggle. You are free in Him. Though you may continue to feel the barrage of that struggle and the temptation to return, rely upon the strength of God, and He will not only give you the resolve, but be the resolve that you need.