I have a 15-year old ESTP cousin, he's been in one relationship so far. He's against cheating, he was taught well, but he did say that the relationship got "boring" really fast, in like a matter of weeks, and the relationship lasted for around two months. He said that it "just ended."
"Are we still going out?"
"I don't know." (the girl)
He's a somewhat shy ESTP, too, but he's told me he's asked out a few girls after being egged on by his friends, rejected each time.
So I figure given the MBTI letters they might be more likely to cheat than others due to being "sensation-seeking" but it still comes down to the person.