Thing I built that only one person uses and I keep paying for

There is a feature in my product that exactly one customer uses. It costs me infrastructure, maintenance, and a little attention every month. The numbers say I should have killed it two years ago.

I keep it because I remember the conversation when they asked for it. They were at a company with a real problem, and I was small enough to actually solve it for them. It was one of the first times I felt like I was building something that mattered to a specific human being.

Now they still use it, and I still pay for it, and I am not sure which is the reason anymore.

There is a version of this that is sentiment and a version that is loyalty, and I genuinely cannot tell them apart. What I do know is that the small losses like this are part of what makes the whole thing feel like mine.

Do you keep anything alive just because of who it was built for? And is that a mistake or the point?