So, my boyfriend....?

my boyfriend and I have been dating for almost 6 months and I love him more than anything. But he has a neighbor. A girl neighbor. She is a freshman and he is a sophmore. They dated before and my friend said that they have been like flirting around with each other. But like everytime I ask my before about it, he says not to worry about it, and when I ask everyone else that say not to worry about it. So my question is, should I just ingore my one friend that tells me all the stuff that my boyfriend does with that one skank, or should I believe her and have a talk with my boyfriend and break it off? Help I am sooooo confused :S