I dreamed that the tortoise wouldn't let go of my hand, and then I had to kill it.

Put it in a pot and let it swim around, which means that you are eager for freedom and want to get the opportunity of freedom like a turtle.

The tortoise bit you, and now you are in conflict with your expectations. If you kill it, you may have given up the same freedom as her, or you may have paid attention to yourself in some things.

I hope it helps you. Dreams are unfinished business in reality. Make amends in your dreams. Don't worry. The most important thing is to face life and struggle. I hope it helps you.