How do you tell someone that your relationship was not meant to be?

So lets say you were a really really really big pothead and during that time you started a relationship with someone who had similar bad habits. After a while you had a kid and straightened up. After your mind resumed to the non-pothead like state from a significant amount of time not smoking and lets say matured a bit you slowly start to realize you don’t really like the person anymore. One day you realize that this person hasn’t changed one bit and you really never liked them very much but unfortunately pot clouded your ideas of what you liked. How do you break it to the person that you don’t have feelings for them knowing that they really want your relationship to work out and they have committed a lot of time and effort to making it work?