I think I had a similar experience to OP. Me and this girl were on and off for a couple of months. Day after sex she always felt distant. I always tried to make the effort - tried foreplay so I could satisfy her, but she never wanted to do foreplay and wanted to jump into sex straight away.
I'll admit, I probably am not the greatest in bed. I have issues with finishing too fast sometimes. But I always tried, and always tried to control it. If I did finish fast, I'd go for another round. Always tried to ensure she was satisfied. The last time, I asked her if she came, she said she didn't but was almost there. I asked her why she didn't tell me so I could have at least tried to.