13 Now listen, you who say, “Today or tomorrow we will go to this or that city, spend a year there, carry on business and make money.” 14 Why, you do not even know what will happen tomorrow. What is your life? You are a mist that appears for a little while and then vanishes. 15 Instead, you ought to say, “If it is the Lord’s will, we will live and do this or that.” 16 As it is, you boast in your arrogant schemes. All such boasting is evil. 17 If anyone, then, knows the good they ought to do and doesn’t do it, it is sin for them.
— James 4
We singles are not allowed to imagine a nursing session in detail. Not with our percieved spouses, or even our bethrothed.
You don’t know if you’ll live to see the next second.
Since dwelling on graphic thoughts of sex is reserved only for married people (1 Corinthians 7:2), and you don’t know if you’ll wake up tomorrow morning, (James 4:13-17), if you’re single, you’re biblically not allowed to dwell on images of the opposite sex’s body parts in erotic detail.