The CEO's Orphan Wife

At the age of fifteen, Myla became an orphan. Her parents friend took her in and treated her like their own child. The family was nice to her, except for Ivan, who seems to be very moody. However, Myla can't help but fall in love with him. 
But Ivan was already in a relationship. One night, Ivan got drunk—waking up next morning besides Myla, leading them into marriage—which Ivan opposed, but his parents wouldn't take no as an answer. The two got married. 
But how would this marriage work if there were three people involved in the relationship?