Overcoming the comfortable stage

Has any girl gotten to the point in a relationship where you and your partner become comfortable? And do any other girls sometimes feel like their partner isn't interested anymore even though he says he still is. How do you get over this? How do you move past these insecurities? How to you just chill out? Pllleassee help. I love my boyfriend more than anything. We live together. We both want a future together. I just don't want to ruin it by always needing reassurance.