How can one protect oneself from Satan and preserve one's faith and guidance after having tasted the sweetness of faith?

What you mention about your state indicates the acceptance of your good deeds in Ramadan, and that you benefited from it. So, praise Allah for this blessing, and ask Him for steadfastness and righteousness. Maintain good deeds for the rest of your life and do not squander the good you have attained. A sign of the acceptance of a good deed is being guided to perform more good deeds thereafter. So, persevere in obeying your Lord, and be sincere in your worship to Him, for He said: (And those who strive for Us – We will surely guide them to Our ways. And indeed, Allah is with the doers of good.)