I had that problem with my ex during our 8.5 years of TTC. Due to this I stopped focussing on it in general and stopped telling him when I thought I was Oing, that way he didn't have a clue that it was the right time to BD. Sneaky I know, but I think possibly the only way. Lots of men feel under pressure to "perform" around O and they don't like it. I hope this helps you.