I signed up to a Thai language school and got my ED-VISA, now I don't want to continue to study, I just want to fly back to my home country but I might want to come back in a few months.

Can I just fly out without re-entry and the visa will be lost?

Do I need to cancel the visa at immigration before? If so, how many days will I have before I have to fly out?

Also, does anyone know if it will be a problem to come back as tourist or get single/multiple entry if I have a cancelled ED-Visa?

And last question Is it possible to make a new ED-Visa in few months if I'll decide to come back and start learning again?

So many questions..

Leaving the country without a re-entry permit will cancel your permission to stay.

Are you on a 90 day entry or on an extension of stay from immirgaiton. Officially an extension of stay must be cancelled at immirgation, with a letter from your school indicating your last day of study. Any day you stay after that is considered overstay.

No problem to come back as tourist or to make a new ED-visa in a few months time.

Thanks for the answer.

I'm on an extension of stay. Sounds like I'll need to cancel it with a letter.

According to what you say I should buy a ticket out asap and then ask the school to issue the letter for the day of the flight?

Yes, that would be best to avoid overstay fines.