Me and my girlfriend have sex a lot. A LOT A LOT.

We hadn't seen eachother in a few days, and she came over today, and naturally, we had sex.

I was on top, which she loves most, and I was going at it really fast and hard (I'm not generally a furious fucker, haha), and she started crying. Me, not noticing this, kept going at my current, furious pace, as she's stuffing a pillow in her face so the whole world doesn't hear her.

I finished up, and she was out of breath and her heart was racing, and I noticed her crying. She told me she didn't get off, but it, "felt so amazing," and how she kept feeling so close to coming, but just couldn't do it, but how even though she didn't, it was some of the best sex she'd ever had.

I don't understand this at all. Not even a little bit. It was "so good," that she cried, but she didn't come?

We've been having sex for a long time, and I know when she's getting off and so forth, and I know she's not a faker. We've been really open and honest about that stuff. Every so often, she doesn't get off, and sometimes I don't.

But please, Reddit, explain this strange happenstance to me.