Just wanna chime in here about 2 interesting points Gordie and Butterfly raised here...
1) Cruise control! That describes PERFECTLY what our marriage before and you know what? Just like that man (Anotherstander?) I felt fine with it as well, and i think that i read somewhere that MEN specifically are often more at ease with that kind of lifestyle since they feel the most secure when they have a "home" meaning a family, a place to call home and secure circumstances around him. It's basically what is necessary to feel comfortable and at ease. Not realizing that your spouse may need something more than that then is probably a recipe for disaster like in my case as well...
2) those "in love" feelings... they DO lessen with time even in a "healthy" relationship/marriage though i believe. After often decades of marriage, that feeling of discovery, excitement and first getting to know a new person is no longer present which is normal. However, the emotional wall you describe is probably the only thing which keeps you from once again feeling CLOSE to that person again, right? I have put up said wall as well and i cannot allow myself to lower it for fear of getting hurt. It also only makes sense to do so with a person that you can see a potential future with, not an MLCer