Samson loved Delilah, but she used him to destroy him. The Lords of the Philistines said to her that she should entice him to discover the secret to his great strength,

And Samson said to her, “If they bind me with seven fresh bowstrings, not yet dried, then I shall become weak, and be like any other man.” So the lords of the Philistines brought up to her seven fresh bowstrings, not yet dried, and she bound him with them (Judges 16.7–8). 

As you follow the narrative, you discover that he uses the number seven again, showing that he placed significance upon it. However, at this point, we cannot tell what significance he put upon it.