The best way is to sit across with the present employer and explain the situation and seek his advise on the way forward without hurting him as far as possible. Better not to take any decision when you are not emotionally stable, either happy or sad. Thank him for the break he had given you and tell him that you would be available in case of any urgent works or as a part time consultant. Discussion is the best way out in such situations.
Thanks and Regards
From India, Hyderabad
Go to your employer and openly speak to him.
Tell him you have got a better offer and would like to move on.
For all you know he may himself voluntarily tell you to move on or give a better offer..
Otherwise give him notice and move on.
He has been helpful but hopefully you also wold have worked sincerely and done your fair bit.
From India, Pune