@-Aincrad- They are not even dating so why should he? It is not like he stared at her like an idiot. He just peeked at her for a moment, don't be so effusive about something like that.
I would get angry if he keep looking at her but if is just a quickglance why not, girls are beautifully and mesmerizing so are the boys and there is nothing wrong with that. I don't monopolize my boyfriend, instead of that I make him to only look at me.