Hi My name is ***** ***** I've been a psychotherapist for 30 years. I'm going to try to help you today with your relationship issue. It is indeed puzzling when someone says one thing but does another. He's told you that he's not sure if he's in love with you anymore and doesn't know if he wants to be in a relationship. Yet you still have a very loving, passionate relationship. I wonder, have you asked him calmly whether he has perhaps met someone he's interested in?
You asked whether it's possible that he has something going on subconsciously that's causing him to question the relationship. It is indeed possible that he is doubting his feelings without really knowing why. He did say that it has nothing to do with you which suggests it's an internal struggle for him.
Usually when someone says "I love you but I'm not IN love with you" they are looking for an exit. I know that's probably not what you want to hear. But in a relationship as long as yours, it would be surprising if he said it without having thought it through for awhile before he actually spoke it out loud--unless of course he's a very impulsive person who regularly says things without thinking. Here's an article on the subject of "what I love you but I'm not in love with you" can actually mean written my a couple therapists. http://www.huffingtonpost.com/linda-bloom-lcsw-and-charlie-bloom-msw/what-i-love-you-but-im-not-in-love-you_b_2885684.html
Can you tell me anything else about your relationship or anything else he's said that might offer a clue? Has he suggested that the two of you live separately? See other people? Has he given you any clues about what he imagines your relationship will be going forward?
Hi again. Just to let you know, I'm stepping away from my computer for a few hours. However, I'll check to see if you've left a response when I return this afternoon.
Hi. I just wanted to let you know that I am still available to discuss this with you further if you like. If the suggestions I've offered so far don't seem to be hitting the mark, please let me know so that I can figure out how to help you better. My goal is to give you excellent service.