Boyfriend sometimes can't finish.

Ash
I love my boyfriend to death and the fact that he can't always cum isn't an issue to me. He is amazing at sex and sometimes it's nice that we can go for so long. But eventually it ends up being I finish and he keeps trying all that he can to get himself off. Usually him jacking off for another 10 minutes. He's been able to come when we have anal sex but only a few times. I feel bad for him because I can tell he's frustrated when he can't. He said it almost feels like it's in the shoot but he can't let it go. Then eventually he becomes numb and it doesn't feel good anymore.. Keep in mind this is after about 30-40 mins of sex. It gets tiring. He hasn't had any repressed sex issues from his childhood so he doesn't think it's mental. But he was in the military for 4 years so he had a long time of nothing but himself. Just any advice on something he can try, or if he might get the ability back. I want him to be satisfied. 
Thanks!