My heart and Brain are at war....?

My Heart and brain are at war..... I love my BF to death, but my jealousy is beyond reach...My heart tells me to trust him 100% but my brain won't.... when i hear that he is hangin out with katherine and stacy, my heart jumps... even THOUGH i know nothing will happen.... but some where in the back of my brain makes me nervous, like oh okay... well why are you hanging out with JUST them??? so can anyone help me??? please only serious answers