Here’s what could be putting you off.
The tip of the penisSee how women wipe after pee’ing? Men don’t, they just wiggle it and that alone doesn’t leave the penis clean. This might leave some odour and in reality licking off someone’s urine is disgusting.
The odour from the testicles… yes, testicles are prone to sweat if not washed properly, and it accumulates bacteria over time. Men usually overlook the area between the anus and the base of the testicles, and that’s where they sweat the most.
Untrimmed pubic hairGiving a blow job on an untrimmed surface can be very unpleasant, hence pubic hair has to be trimmed very often. Hair shafts collect sweat and dead skin cells which can turn into an infection and nobody wants to put bacteria in their mouths right?
He could have masturbated just before sexIt’s very important that he washes with a mild soap and warm water each time after pleassuring himself. Semen dries up after some time and can have really bad odour if left unattended.
What you can suggestDepending on where you’re having sex, you can suggest that he use’s a wipe, or make an adventure of it by starting off in the shower. You’ll have no disgusting thoughts running in your head while giving him a blow job.
If this is a problem you’re facing in your relationship, adress this during a non sexual time and come with medical and health information as back up. In the end you’re not only looking out for yourself but for him as well.