why does he keep coming back?

me and this guy have been friends with benefits for 8 years and he’s had girlfriends and cheated on them with me (at the time i didn’t know he was in a relationship) sometimes we don’t talk for weeks or months and then out of the blue he hits me up!! why does he keep coming back? i always let him back in and i’m not sure if it’s because he knows i will or if it’s something more than that!! it’s been 8 years and i can’t wrap my brain around the fact that he always comes back to me...help!!!