If I were in MX's position, I'd be a bit uncomfortable doing much beyond hand jobs if you had a partner with such potentially unsafe sexual behavior.
As it is in my relationships, people don't go beyond manual stimulation until everyone has shared recent test results, and if new people are coming into the picture for any partners, their results need to be known too.
My girlfriend's boyfriend's other girlfriend needed to see a print out of my results before I could do oral with my girlfriend. My wife and I appreciated her safety consciousness, as it makes us feel more secure that that branch will remain safety oriented with future partners as well.
As others have said, CS DOES already have equality, but he wants more than that. If I were to give him any credit, it would be that while your relationship has been open for quite some time, this appears to be his first time experiencing you being with someone else, while you've had numerous chances to get used to him being with other people, so it makes some sense that you appear to be much better at it at this point.