No clue why, but the smell/taste of semen makes me gag

I absolutely love giving my guy oral. The sounds he makes and the things I can do with him are amazing and I love giving him the best orgasms I can.

He loves it when I swallow and has been asking if I'm gonna do it again.

I gladly would; however, the smell and taste of semen is absolutely repulsive to me and I get nauseous. I really wanna swallow, but I'm afraid that, if I do, I'll puke and would rather not ruin what should be a great moment. (I swallowed earlier in the relationship, but just can't do it anymore. Almost gagged back then, too, but it's gotten worse lately.)

I can't even lick it up and, when he ejaculates on my chest, I get nauseous from the smell.

He's been eating healthier these past couple weeks and I think it's gotten slightly better, but it's still nowhere near good.

Does anyone else have this problem? How do I explain this to him without disappointing him? Is there a way to get around this general aversion to semen?