And, what if... Your partner cannot get his li'l buddy to stand up?
It doesn't have to be the end of all sexual intimacy. It's important to make him understand that he's allowed his dick to define him a tad too much. Prove to him how much you still appreciate him, how much you still enjoy playing with his pecker; how much pleasure he can still derive.
A partner in a seminar never got the least bit hard as we went through an hour-long exercise. At the end, he apologized for not getting a boner. I assured him it didn't matter to me; I had a terrific time and hoped he enjoyed what I did. He admitted he did - more than he'd expected.
Consider signing up for the couples Body Electric seminar. They'll teach him how to orgasm without a boner, without shooting a load of cum. In the meantime, take your man with the limp noodle... Have a nice romantic dinner. Then take him by the hand, lead him to the bedroom and undress him. Take your time, stop to enjoy each part of bare skin you expose. Undress yourself, slide under a warm shower together. Wash each other from head to toe. Head to the bed, or the floor, or the kitchen table even! Give him a nice, slow, soft, gentle massage. Play with his cock, rub his balls, massage his pecs and play with his nipples. Deliver small, wet kisses everywhere.
If he gets frustrated, maybe turns away and begins to balk because his cock isn't going to respond, tell him, "I don't care. A solid steel stiffy and gobs and geysers of blasting jizz are not necessary. It doesn't have to be hard for me to love it anyway! I love touching it, playing with it, sucking it." and prove it!
Show him just how much enjoyment he can still get out of his cock; how good it can feel, how nice it feels to have attention paid to his balls.