Okay. Deep breath.
If a man loses his erection before sex does it mean he doesn't fancy his partner any more?
If it happens a few times, doesn't it mean that he doesn't??
My DH doesn't smoke/drink loads/isn't especially stressed, none of those "usual" reasons I've heard about.
I am very upset about it, he won't talk to me about it, and I have decided it's because I'm too old/fat/have a scar from a big operation and he just can't bring himself to do it anymore.
If he won't explain to me maybe a MN man can!