Zero sex drive

I'm 25f and my partner is m37.

Last year was the hardest year of our relationship (three years) because his sex drive dropped off which turned out to be because he was watching a lot of porn and coming to that. We managed to get through it and had great sex once again for the last 6 months however he still cant cum PnV styles and only by me going down on him.

Recently I've got a second job and am so exhausted that sex is the last thing I want to do especially when I have to blow him for at least 20mins before he cums.

We haven't had sex in 27 days and tried tonight - I went down on him and he didn't cum. I think he must be watching porn again because surely after 27 days, a man would cum from a BJ!

How do I approach this in a nice and caring way?