I wouldn't even feel guilty, provided your man luh-vah isn't self-conscious or frustrated about it.
Let's flip the situation: women are famously complicated when it comes to trying to give them The Righteous O. It's like every woman has her own sexual PIN number that each guy has to figure out. It takes patience, communication, and commitment. Quitters never win. It can take weeks or even months to discover exactly how she needs it. Sometimes, she doesn't even know exactly what it takes. But oh the rewards, especially when the dude finds out that three strokes there, a pinch here, and a pillow under her butt is all it takes to make sunbeams and rainbows shine out of her secret lady place.
Of course, not everyone is the same. I've been with women who can get off so easily, all it takes is a rakish wink at their clitoris. And not all men are permanent fifteen year olds: stress, a drink or two, or a kinky little trick they're embarrassed to share can stand between them and being able to pop the cork. Human sexual response is not an exact science. For some people, an orgasm isn't even the most important part of the process. There are men and women who enjoy the journey more than the destination.
If it gets to the point where it's wounding your ego, or becoming an issue in the sack, I would first recommend not making a big deal about it. I would then do something very simple: watch a porno with him. Study how he gets aroused, and more importantly, what he does once that has happened. Like a Scientist of Love, observe him pleasuring himself. Get an idea as to what it is that really turns him on, explore his rhythms, learn how he does the job.
I've given similar advice to men concerned about not being able to bring their women to climax. If anything, it's a good, healthy start.
Besides, guilt is a waste of time.