What is the ruling on a man masturbating using his wife's underwear for arousal, and is this considered an imitation of women that incurs a curse, and what is required of him for repentance?

Masturbation is not permissible; it is a forbidden habit.

It is forbidden for a man to imitate women, and that includes wearing their specific clothes, whether with the intention of imitation or not.

Repentance from this involves abstaining, regretting, and resolving not to return to it.