Unsubscribe Management in Nurture Programs

We are sending to our customers regularly through a nurture program when they are in a trial period. Right now if someone chooses to unsubscribe from this nurture program, the form is working, and field indicating that they want to unsubscribe is correct, but we have having trouble preveting the email send when someone is in the middle of a stream and still has more emails on the stream to recieve.

For nurture programs, what is the best way to unsubscribe someone from the lists if they request it?