It's kind of strange. Once we get past learning to trust people, we settle into routines, patterns, and expectations. We come to expect the things that the person has been providing. We lose sight of how precious and important this person is to us. We start to take them for granted. We figure no matter what, they will always be there. We neglect them. We figure I'll focus on my deadline at work, my kids, etc. My relationship is strong, it can handle it.
In counseling people after they have gotten a divorce, I have heard variations on the same story time and time again: "I figured if I worked all the time for just another year we would be fine." Or, "She told me she wasn't happy and that we never spent time together anymore, but I figured we would get through it." They continue, "And then one day they just left. They said they were done." People have emotional needs and once they go through enough loneliness and disappointment, something inside of them shifts and they are not able to do it anymore. Finally, the person then looks at me soulfully and says, "What happened? How did I get here?" They got there by taking someone they loved for granted. It happens with mates, kids, friends, and parents.
Sorry for the somber note on Thanksgiving weekend. But this year consider not taking any of the people that you care about for granted. It requires time and re-prioritizing. It may be inconvenient. Think of it as an investment in the people that are precious to you.