In the story, Samson is said to lose his power when his hair is cut, breaking his vow.
I think he was wrong about his hair, and the actual source of his power was his love.
I think he lost his power the moment he realized Delilah had betrayed him.
Not when she betrayed him, nor when she cut his hair, but only once he realized what she had done, see?
So at the end of the story, when Samson gets his strength back, it happens not because he grows his hair, but because he forgives Delilah.
His hair was only a metaphor for his faith (in God, love, women, and Delilah in particular)...
Anyway, I'm growing my hair out.
*Edit - I wanted it to be clear this was about forgiveness, not betrayal. <3
Disclaimer: I'm not religious, but I grew up going to church and Sunday school, etc.