I mean if I want to use this 3 times on someone to bring him to defining admiration to me I have to increase the strength of the... Argument? Evasion?
Yes. It's fair game to do that entirely with stunting in combat, as long as the Storyteller thinks your escalation makes sense. Same goes for in-combat intimidation.
Do I also have to use the leverage of an other intimacy to do so above the first instill which created the initial minor intimacy ?
As usual, escalating Minor->Major requires leveraging a separate Minor+ Intimacy, and escalating Major->Defining requires a separate Major+ Intimacy.
Can the fool who wronged me use Willpower to prevent the minor intimacy to be created?