orgasm disappeared

I've been with this guy for months now and in the past he has always been able to make me orgasm multiple times. Sometimes even one right after another to the point I use to lose count. Lately it seems like when we have sex it feels amazing but I can never reach that tipping point. Our relationship changed a bit but I can still get off just thinking about him when it's just me but when we have sex it's like I start to head on the right path and but doesn't get close. I don't get it why the sudden change? Why does it still feel good but I can't orgasm anymore?