Judge him by his actions, not the way he looks at you. Some dudes, especially the slick ones (like how I was in college), could totally convince any girl that she's THE ONE.
That was how I took all those v-cards in college....too many to remember. Those girls were usually very insecure and inexperience, so I was able to manipulate their feelings.
Once I slept with them, I would lose interest and move on. Yes I was a jerk back then, and I have changed completely. Would never want to deceive another girl again.