He knew. He knew something wasn't right about that Alejandro guy. And it's not because of the fact that every girl, excluding Sierra of course, is fawning over him instead of Justin. Ok so it is but not entirely. Ever since he got voted off he would watch every episode and saw how selfish and self-centered Alejandro is. He's flirting with almost every girl and one-by-one they get voted off. Unlike him, Justin would never make any girl act out with how he talks. That was the whole reason why he rarely talks; he didn't want to end up using a girl like that for his own selfish gain.
Another proof was season 2. He may seem to be an antagonist at that time when really he's trying to make sure no girl gets swoon by his voice and get the wrong message. Causing heartache is the last thing he wants. Especially her; Heather.
Out of all the girls, Heather was the one who smitten him. After World Tour, Justin found something shocking; Heather crying. As it turns out she had also fallen for his charms but as it turns out she was just a pawn to his game and when he was done playing with her, he threw her away. Now here she is right in front of him broken and crying her heart out not caring if someone sees or hears her. She was crying over someone who just used her for his own gain.
Unlike the other girls who have boyfriends, she didn't have anyone to love or be loved by. But that was years ago, this is now. Justin still hates him with everything he has to this very day. However, he'll have to thank him for it. If it weren't for him he wouldn't be where he is; a good home, a great career as a male model, and with a beautiful wife no matter how round she gets.
Tonight, he is lying with Heather. His hand is on her plump belly, feeling for the little pitter-patter of his child's feet. He put his lips on her belly before moving up for her luscious lips.