The mor things change the more they stay the same

well once again i found myself opening the door for him again.  this is a vicious cycle that we have fallen into.  me and aaron which is my on again off again boyfriend for the past two and a half years, have been fighting more than usual lately.  it never fails when we do he leaves and about two or three am he comes knocking on the door saying he misses me.  i and ofcourse me being the idiot that i am i let him in.  we are like magnents and gravitate to one another no ,atter whats going on between us.  i love him very much but i can not do this anymore.  if anyone has any advice i would love to hear it.