Do all boyfriends check out other girls than their girlfriend?

well my boyfriend says he doesn't check out girls and that I should believe him. when I am with him he does look the other way if a girl does come, but at times I feel like he does look at other girls. but I wanna make sure he doesn't lie to me if he has I wanna know how I can make sure he is telling the truth.
Do all boyfriends check out other girls than their girlfriend?
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