Should i start a relationship with my teacher when i leave. Im18 and i believe she/s attracted to me too?

I think you are right when you say wait until you leave and then ask her about if she likes you. My advice would be, wait until you leave, then ask her about it and if it turns out she does then good for you, there would be nothing standing in your two's way. If she doesn't then theres no problem with that, you were only asking xox