I remember reading it on Rain of Snow but now I can't find that novel... It's somewhat similar to the premise of "I Slept with the Villain Holding My Hand". Except they really slept together. From what I remember, the MC also has platinum/silver hair, she's a princess and her brother's the crown prince. The ML is a duke, the original ML is also another duke. The MC's also friends with the original FL. The FL doubts whether the ML really likes her for a while and even sent him to war to get away from him. The ML's kinda obsessive. That's kind of all I remember ;-; please help.