Is there a word in English for someone who likes to experience something which has somewhat been experienced by himself already?

single-word-requests

For example someone who has bought a cellphone a week ago but now wants to change that and buy a new one; or imagine someone who wants and likes to have a sex with a woman or a man first he wants a tall one and just after the first or second sex he or she gets bored and wants a blonde one and then brunette and after that slender and so on . And I want to say someone who gets bored with having or doing something too soon.

To be clear, imagine someone who isn't going to be satisfied with something he has or has experienced already and wants to have and experience something else which he thinks it is better. There is a word fickle that is kind of similar to what I mean, but the definition is not what I'm looking for.

Although your question suggests that they are trying to experience the same thing again, each iteration sounds new; a new phone, a different person. At that rate, I'd propose:

Novelty seeking behaviour

I realize, this is not a single word, so you could amend it to: novelty-seeking. https://en.wikipedia.org/wiki/Novelty_seeking

"Neophilia" is defined by Oxforddictionaries.com as "love of, preference for, or great interest in what is new; a love of novelty". From this, one might proceed to "neophile". Though this last is a less common usage, I did find a definition for it at Collinsdictionary.com, as an alternative form of "neophiliac".

You might consider insatiable