When you go to bed and wake up with a person everyday, you're at least spending one third of your life with them— aware or not. That's probably the reason that married people become more and more like each other with every passing day. Their minds are melting together as they sleep, forming one single consciousness. Like when people say that dog owners look more and more like their dog everyday, the same goes for spouses. (Not saying that your spouse is a dog or anything)
Married people just spend too much time together! Slowly but surely, they acquire every fact about their spouse, read their minds, and eventually anticipate their needs before they even realize it. They've seen you dressed to the 9's and looking like a baddie, but they've also seen you with peanut butter stains on your sweat pants— life is all about balance. Whether you like it or not, that's true companionship.