The previous people to answer this have assumed you are a woman asking if a boyfriend might be gay. But why shouldn't you be a gay man asking if your boyfriend might be straight? But that seems very unlikely, because why should a straight man go out with another man and pretend to be gay? But then again, in this day and age when there is no stigma attached to being gay, why should a gay man go out with a woman and pretend to be straight? So, my answer is - whether you're a man or a woman - just accept what he says he is, until you have any real reason to doubt it.