If you are 17 and sleep with your teacher and continue this relationship that is then reported by someone who is not you or the teacher. If you did not want to press charges, would the teacher still be aressted for felony?

Yes, he or she could still be prosecuted.

Whether a crime is prosecuted is up to the prosecutor (the state), not the victim.

First most likely teacher will lose job.

But yes, teacher will most likely be charged and arrested.

first most likely teacher will lose job.

but yes, teacher will most likely be charged and arrested.

In many states. But whether it's a crime will depend on state law, which varies from state to state.

I believe you are in the UK (Any question on law needs to include your general local as laws vary by area)!

However, I think this is pretty much standard. Its up to the prosecutors whether they want to prosecute a crime reported to them. They do not need the victim to press charges.