So. Kids.
Before my wife and I got married, we were both "on the fence" about having children. We'd discuss the prospect, and ultimately came to the decision that we wouldn't have children, but we weren't completely shutting the door on the possibility of having them either. After we got married, though, we've been gradually settling on different sides of the fence. Three years into our marriage, and I'm now very sure that I don't ever want to have children. She's been showing strong indications that she's starting to want to. For example, "Hey, so-and-so just had a daughter, wouldn't it be great if we had a kid too?" Or "Hey, your uncle and your grandma have been asking about when we're going to have kids, maybe we should get started so they'll shut up." Or "Hey, I'll bet our kids would be really cute."
For my part, I don't want to have kids because... well... why should I? What's the point? I feel no biological desire to procreate. I don't think it's necessarily a stage of life that I need to go through. I certainly have nothing against children, or people with children, and I can interact with other people's kids without any problems. But I just don't feel the need to have any of my own. Furthermore, I don't feel ready in any way to be a parent, whether it's financially, emotionally, etc. I think it'd be rather irresponsible of me to bring an unwanted child into this world. We also both have stressful jobs involving long hours, and it's hard to envision where we'd find the extra time and effort necessary for a kid.
However, every time I've asked my wife outright whether she wants to have kids, she'd say she's ok with not having them. I think she realizes that I've thought this issue through, and that I feel rather strongly about it. So she's avoiding the issue by humoring me. But I'm worried that she does want them, and that she realizes there isn't really a compromise to be found here (you can't have half a kid), so she's afraid of the logical conclusion that this road would take us. And yet, avoiding the issue doesn't help anyone. What if, fifteen years down the line, she ends up with tons of resentment because she feels like she had to do what I wanted, and sacrificed her chance to be a mother?
I don't think this is anyone's fault. We were both honest about how we felt before we got married, and we were on the same page. It's just that over the course of the last three years we've gradually settled on different sides. It rather sucks.