Here's the thought that goes around and around: everything works when I'm alone, so it can't be a problem with my body. Then why does it fall apart the moment someone else is there?
It's one of the most confusing parts of this, and it's also one of the best clues you have.
What changes when someone else is in the room
Chapter 1 of Performance: Unlocked makes the point directly. Performance anxiety can show up even when you're physically fine. Many men can get aroused alone or in certain low-pressure conditions, then struggle when attention shifts to evaluation. That doesn't mean the solo situation is "easier" in some deep way. It means it has fewer triggers for self-monitoring. When the environment doesn't demand proof, your system can do what it's built to do.
With a partner, new questions arrive without being invited. Is she enjoying this? Is it taking too long? What does she think when I pause? Each of those pulls your attention out of sensation and into judging, and judging is the thing your nervous system does badly while aroused.
Why this is good news
If your body works fine in some settings, that points toward the attention-and-threat explanation the book describes and away from something fundamentally wrong with you. It isn't a promise that nothing physical is ever involved, and I always say a doctor is the right call for persistent trouble. But the pattern itself carries information.
What to do with the clue
Look for what's different between the two settings, and be specific. Is it being watched? The sense of consequences? Time? Wanting to please her? Once you know which cue is pushing you into evaluation mode, you can aim at it. If it's being watched, the pause signal and a bit of partner communication in Chapter 7 take pressure off. If it's consequences, the Green Check work in Chapter 3 helps with the "this means something about me" story. If it's time, the preparation protocol in Chapter 8 shrinks the "what if" window.
A small experiment
Next time you're alone, notice whether you're checking or feeling. Most men find that solo moments are mostly feeling. Then compare that with a partnered moment, and try to catch the first instant you switch. That switch is the thing the book teaches you to catch.
The chapters walk you through this pattern one piece at a time. Performance: Unlocked is in my Shop, $39, instant download.