Honestly, if it was me, my doubt would skyrocket after she became 'honest'. MC's house might still be small, but they're already on the rise, and here comes a girlie with insane politics and ambition, who decided to place her bet on you. Being ambition doesn't mean she'll betray you, but liking and choosing you now doesn't mean she won't stab you later. Important thing is, for her, it's totally calculated. Also, who's to say she's not acting even now.
But meh, what's one more? He might get stabbed by his li'bro anyway. 😜