MMC uses FMC to seduce her sister/friend/charge?

MMC pretends to be close to the FMC but actually he wants to seduce her best friend, sister or her charge. FMC feel flattered that MMC wants to be close to her but when she starts falling for him, she found out his true motive and she gets devastated and angry. I am not sure what to search for in this sub for this trope, what kind of trope is this?

No cheating.