Clint always kept his eyes on you, and not in a creepy way, but a way where he was always looking out for you. You are his girlfriend. But when Clint was watching you from up top, watching you talk to some good looking tech guy, he got jealous. He saw how you smiled at him and the laugh you gave probably after a horrible joke he made. And when Coulson called him over the comms, it was hard for him to pull away.