No chemistry

Just a short rant... when we first started dating the sex was great and hot and lasted a long time and he could usually go 2 or 3 times. After like 3 or 4 months it started to go downhill. We talked it out and it got better then it went back down. Now we barely have sex and when we do, it's like 2 minutes and he doesn't finish me and it's not exciting. I miss how it was. Every other aspect of our relationship is amazing bit there's just no sexual chemistry anymore.