I cum in 8-9 strokes

When I’m alone and practicing edging, I can control myself pretty well. For example, I can edge for around 20 minutes without reaching the point of no return.

But when I go to my girlfriend’s place, things are very different. Just touching her makes me extremely aroused and I get a very strong erection. Sometimes I go down on her first, and while I’m doing that I’m already very hard and very turned on.

The problem is when I finally penetrate her. After I enter, I usually ejaculate in about 8–9 strokes. It happens very quickly, even though I had good control during edging by myself.

So I’m confused about why this happens. Is it just because of higher arousal with a real partner, or could there be something else going on?

What is happening?