Suddenly my stamina has decreased. Any ideas?

For most of my life (39), stamina has never been an issue. I’ve always had pretty good control, and actually had the opposite issue in my mid 20s for a while, where I lasted too long. If I started feeling close, I’ve always been able to either change positions, adjust tempo, or focus on something in the corner of the room to distract my mind just enough to hold off ejaculating. I even regularly masturbate to “clear things out” like I’d do when I was single and pretty sure I would have sex on a date that night. If I’ve been drinking, even, which historically also delayed my ejaculation, doesn’t make a difference. Doesn’t matter position, state of mind, frequency from last time I came, nothing seems to delay me. Has anyone had this issue suddenly start, and how was it fixed?

Other bit of context, been only with my wife for 8 years. She’s done nothing different, our sex life is pretty active, I’m content and attracted to her, and it really feeling like I’m lacking anything from her.