I completely agree that David should have pulled her aside and spoken to her about her decision before he made his. Maybe she wouldn't allow that. Maybe the other girls wouldn't allow that.
David deserves someone that likes him and is willing to stand by him or follow her heart or
She's not willing, she's easily influences, she's weak, etc.
What the hell would she do when she realizes this is all fake? My guess is she sure as hell wouldn't stand by him. David deserves someone stronger than that. Hopefully he'll find that with some of the remaining girls.