A few more thoughts I had as I tried to empathize with your H.
1) He may still be so emotionally fused to you that he feels like you are rejecting him when you reject his semen.
2) If his feelings about the "semen swallowing" are like my feelings about the "gym sheen" then he may be thinking along the lines of what I actually said to my H when we tried to communicate openly about the issue. He told me that he really had a preference for not having "after gym" sex because he didn't like the taste of salt on my breasts. I told him it bothered me when he told me about these kinds of preferences because it made me feel like he was constantly having critical thoughts about the experience when we were having sex and it turns me off and makes me self-conscious to imagine my partner having those kind of critical thoughts.
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver