okay so i had this same issue with my boyfriend of 3 years... after about two and a half years he cheated because the realtionship started to get boring and dull and we both were not into it anymore. what i suggest is TALK TO HIM ABOUT IT. tell him that your starting to feel "too comfortable" and you want to do something to change that. try to do something spontaneous that will spice things up. no i dont just mean sexually, i mean even something silly like just spending a night in a hotel room just for no reason. or something else that you have never done before. just dont wait too long because if your not into it, he soon wont be either... and you dont want him or you making a mistake and ruining the relationship because your not happy or like i said your too comfortable.. 

hope this helps ! 

brooklynn